Jo was well used to travelling in The Doctor’s souped up vintage car, Bessie, by now. That was why she was wearing a snood. It covered her hair and came snugly over her forehead and up around her neck and shoulders, too. Any other hat would have been left behind on the road when The Doctor pressed the button in the middle of the dashboard that turned an ordinary internal combustion engine into jet propulsion and allowed the little car to leave the U.N.I.T convoy a mile behind them.

“Travelling by military convoy, indeed!” The Doctor commented dismissively as he slowed the car back down to a relatively normal fifty miles per hour. “In any case, I’m sure this is going to turn out to be a big panic over nothing. U.N.I.T go tearing about the country at the drop of a hat and expect me to join their circus parade.”

“The message did seem quite urgent,” Jo pointed out. “A whole building disappearing into thin air... That’s quite unusual. I do hope it isn’t Omega again.”

“It might not be anything,” The Doctor said. “They probably just mislaid the building. You know what the bean counters are like. The Atrantian Civil Service once mislaid an entire planet. Just a clerical error, of course. The planet was right where it should be. They kept the accounts, all the same. Three hundred years later when they realised their mistake, they sent the whole population a demand for back taxes.”

Jo wondered if she ought to believe a story like that or not. She was never entirely certain with The Doctor.

“So you think we’ll get there and they’ll have found the building, after all?”

“Very likely.”

“But what if they don’t? It must be some sort of alien activity. Do you have any idea what sort of aliens would steal buildings?”

“I wish you would say ‘extra terrestrial’ rather than alien,” The Doctor chided her. “After all, you’ve been to other planets. It’s like English people going to other countries and calling the local people ‘foreigners’.”

“Whatever. But which ‘extra terrestrials’ steal buildings?”

“I’m not aware of any that do it for commercial purposes, or for a hobby, for that matter. But I know there is technology that can do that. A h2o scoop would do it. Or a very powerful transmat beam. There are some very rare species with telekinetic skills that would be up to it if they worked as a gestalt. But why would anyone with that sort of technology want to bother with a research facility outside Cambridge, England?”

“To use the knowledge, of course,” Jo argued. “There were loads of scientists in the building. They took them to use their knowledge.”

“Anyone capable of using a h2o scoop or wide range transmat doesn’t need anything that a Human scientist in the twentieth century knows. They’re already far in advance of Human endeavour at this stage in your history. Of course most sentient races ARE more technologically advanced than humans. The dark ages severely held you back in your development. ”

“Oh well,” Jo said. “That’s us, the slow kids of the universe. So what ELSE could they possibly want to steal a building for?”

“I expect we’ll find out when we get there,” The Doctor replied. “Assuming it isn’t just a clerical error.”

Their destination was the Bracewell Insitute, founded in 1945, so Jo read in the U.N.I.T report, in memory of a brilliant scientist who had worked with Winston Churchill himself on secret defence projects but was reported dead during one of the worst nights of the London Blitz. It was on the outskirts of Cambridge, and wasn’t, in fact, one building, but three, built around a triangular courtyard with a futuristic sculpture in the middle.

The courtyard with its sculpture, identified by The Doctor as a representation in cast bronze of the Human genome, was all that currently remained of the Bracewell Institute. The three buildings were missing – at least the part of them above ground, anyway. Their foundations remained. Basement rooms housing huge computer servers, boiler rooms and archive storage had being hastily covered with canvas sheets in case they were rained on. The personnel who were lucky enough to be in those basement rooms when the buildings disappeared were currently being housed in a large tent and serviced by a NAAFI mobile kitchen from which refreshments were provided. The army had the area in lockdown pending the arrival of their specialists from U.N.I.T.

As the first of those specialists to arrive, The Doctor and Jo were shown into the tent and introduced to the senior scientist who was still available.

“Doctor!” Professor Elizabeth Shaw greeted him with a wide, welcoming smile and a firm handshake. “It is good to see you, at least. Perhaps we’ll get to the bottom of all this, now.”

“Good to see you, too, Liz,” he replied. “May I introduce Miss Jo Grant who is assisting me in my work.”

“Another female scientist?” Liz Shaw asked as she shook hands with Jo. “I am amazed. There aren’t many of us about.”

“No, I’m afraid not,” Jo replied apologetically. “I only took A-level science. And I failed that. Besides, what would be the use of another scientist around The Doctor? He knows everything... or thinks he does.”

“Oh, don’t tell me!” Liz answered her with a conspiratorial wink. “But... Doctor, you’ll want to know everything, of course?”

“Anything you can tell me,” he said. “You weren’t in the building at the time?”

“I was in the basement,” she explained, stepping out of the tent and pointing to the foundations of what had been called The Hypotenuse because it was on the long side of the right angled triangle.

“Lucky for you,” Jo commented. “If you’d been in your office you’d be missing, too.”

“My office IS in the basement,” Liz responded with an edge in her voice that spoke volumes about being a woman in a profession dominated by men. “So is my lab. I was working on a... well, it’s classified... and it doesn’t really have anything to do with what happened. Suffice to say, the experiment was ruined when the ceiling disappeared and everything was exposed to the sunlight.”

“The ceiling... or the floor of the building above you... just disappeared?” The Doctor questioned her. “It happened instantly? Was there any sound?”

“Instantly,” she answered. “And there was no sound at all.”

“Curiouser and curiouser,” The Doctor commented. He took out his sonic screwdriver and used it to analyse the foundation walls that remained and the ground around them. “Ah... interesting. Very interesting.”

“You’ve found something?” Jo asked him. “Radiation? Residual energy...”

“I’ve found absolutely nothing,” The Doctor answered. “That’s what is so interesting. There is NO radiation, no residual energy, not one single ion particle. You always get ion particle residue from a transmat. It’s what gives people blinding headaches when they travel that way. But there’s nothing. No obvious technology was used to remove the buildings from time or space.”

“What about the... what did you call it... h2o scoop?” Jo asked. “I might have failed science, but I do know that h2o means water.”

“It wasn’t that,” The Doctor replied. “Liz would have mentioned a torrential downfall localised on her suddenly exposed laboratory.”

“Er... yes, I think I might have noticed that, as well as the missing building,” Liz confirmed. “So you don’t know what did it or if it might happen again?”

Liz sounded disappointed. Jo thought she understood how she felt. The Doctor usually had some spark of an idea at this stage in an investigation. With nothing from him where else could they turn?”

Then they were distracted by two things happening at once. First, the U.N.I.T convoy finally caught up with The Doctor and Jo. A Land Rover halted beside the foundations of the Hypotenuse. Brigadier Alasdair Lethbridge Stewart climbed out of the passenger seat closely followed by Sergeant Benton who had been driving him. Liz Shaw smiled wryly at the two of them.

“Talk about the bad pennies,” she said. “Really, what do you think the military can do in this situation? It’s The Doctor we need.”

“You can’t have him without us, Miss Shaw,” Benton answered. “Besides, if there ever was a situation that needed containing, it’s this. We turned back two TV news vans heading your way. BBC and ITN. You really DON’T want this going nationwide, do you?”

“I suppose not,” Liz began. “Even so...”

Then everyone’s attention was distracted by a flash of bright light and a scream that seemed to begin halfway through, as if the screamer started off in a different place entirely and finished here. Everyone turned at once to see a woman in military uniform appear about eight feet above the tarpaulin covering Liz Shaw’s laboratory. She ‘hung’ in the air for a fraction of a second before falling onto the tarpaulin. Fortunately it was thoroughly pegged down and took her weight, but it was a less than dignified scramble to the edge before Sergeant Benton reached to help her onto solid ground. When he did so, and she replaced her beret that she had clung to during the scramble, he saluted smartly before bringing her to the Brigadier.

“Sir,” he said. “This is Captain Erissa Magambo, of U.N.I.T.”

The captain saluted again. The Brigadier reciprocated. Since he outranked her he didn’t have to, but there was something about her arrival that suggested she had earned a salute at the very least.

“U.N.I.T?” He looked at her cap. It was red and the cap badge showed a map of the Earth inside a circle with wings either side. The cap Sergeant Benton was wearing was pale blue with a circular badge with no wings.

There was something about her uniform, too, that wasn’t entirely right. It was a different style to those worn by the women under his command, less feminine, more unisex, as if the army had recognised that a soldier was a soldier regardless of gender.

Plus the fact that she was coloured. The Brigadier could count the number of coloured commissioned officers he knew in the whole British Army. As for a coloured woman with rank...

“You’re... from the future...” he said. “The FAR future, it must be.”

“Yes, sir,” she answered. “2012. And this... if our calculations are correct... must be 1972?”

“It is.”

“Then I made it. Thank heavens for that. You... must be Brigadier Lethbridge Stewart. It is an absolute honour to meet you. And...” She turned to look at The Doctor. “I know you, sir. I’ve read all of the files. I’ve reason to be glad of your genius more than once. Though... of course, that’s in your future, as well. I’m just glad to have found you. That was why I risked the experimental time jump. We had to find The Doctor. We had no way to contact the version of you from my time. But we knew you’d be here, now.”

“Very clever, Captain,” The Doctor said. “But does this mean you have information that will help us find out what happened to these buildings and the innocent people inside?”

“I have,” she said. “I’m afraid the information includes a list of casualties, though. We really ought to go to your mobile command centre, Brigadier. This is all highly sensitive. My presence here is a national security issue, let alone anything else.”

“Of course.” The Brigadier was still slightly reeling from the Captain’s arrival, but his men had been getting on with the job. Already the command centre was set up in the back of an articulated lorry in military khaki. Long coils of telephone wires were being reeled out towards a junction box where they would be connected to the network. Computers were powering up, their reels of software whirring madly. Everything was in place for a thorough military operation.

Even tea was on hand. Captain Magambo sipped a cup gratefully and opened up a file she brought with her in a leather pouch. The first page was, as she said, a list of the dead. Liz Shaw viewed it anxiously and gasped unhappily at the number of names she recognised.

“What happened to them?” she asked.

“In 2012 the Hypotenuse is still there, still being used as a research centre. The building from 1972 rematerialised in exactly the same place... the same place as the existing building. But there was furniture in different places, computers, and... people materialised THROUGH solid wood, walls, electrical appliances. The lucky ones died instantly. Some... lingered. It would have been much worse but a fire alarm sounded a few minutes before. All the 2012 personnel had evacuated the building. They were safe.”

“Who did that?” Jo asked. “Was it a lucky coincidence or did somebody know...”

“We don’t know. But we think we DO know what happened to cause the disastrous time anomaly. I’ve got the data here...” She gave the file to The Doctor. It contained page after page of data printed in hexadecimal code, the language of computers. “It was the only format we could be certain of surviving the time jump,” she said. “All the computers from 1972 were completely fried. All the reel to reel storage tapes were wiped. Our people concluded that there was a massive electro-magnetic pulse that ruined any kind of data storage.”

The Doctor said nothing. He was too busy reading through the pages. Liz and Jo both looked over his shoulder and gasped in astonishment. Liz was a highly educated woman who understood almost every branch of science, but she couldn’t read hexadecimal. To Jo it was just gobbledegook.

To The Doctor it was a scientific formula and it made perfect sense to him. He murmured under his breath and occasionally said things a little more loudly like ‘of course, that would work if the gyroscopic accelerator was primed correctly’ and ‘absolute genius... for a Human’ and less coherent scientific phrases.

“Doctor?” Jo touched his arm as he spoke to him. “Doctor... what is all this?”

“It’s a formula for using wormhole technology to transport solid matter through time,” he replied. “Somebody was experimenting with it here in 1972 and accidentally triggered the disappearance of the Institute. There are notes here from somebody else in 2012, a Professor Malcolm Taylor, who had been working on refining the project. That’s how he sent you back to us, Captain?”

“He was ready to go himself, but I convinced him that he should stay with the wormhole creator machine, in case he was needed.”

“Mmm...” The Doctor frowned. “Are you sure that was wise? A scientist with this sort of hands on experience of the problem might have been more use to me here than another soldier. I have plenty of those.”

“Believe me, Doctor,” Captain Magambo assured him. “You want at least four decades or a wormhole in time and space between you and Professor Taylor. He’s... hard work.”

“Indeed? Well... I’m certainly grateful to him for this. But it’s useless on paper. The information needs to be transferred to a computer. And a powerful one, at that. Brigadier, I need...”

He turned and smiled. The TARDIS was just being put into position inside the command centre by four U.N.I.T men. He grasped the sheaf of papers in one hand and reached for his key in the other. He stepped inside followed by Jo, Liz, the Brigadier and Captain Magambo, with Sergeant Benton bringing up the rear. He turned and looked at them all irritably.

“I can’t do anything more until I’ve typed all of this lot into the TARDIS databanks. Buzz off, the lot of you.”

The Brigadier and Benton did as he asked right away. Captain Magambo took her time, gazing around the console room wistfully. Liz and Jo stayed put. The Doctor looked at them both pointedly.

“Well, you didn’t mean US, surely?” Jo protested. “Come on, Doctor, there must be something we can do?”

“And if you suggest either of us can make the tea, it will go down hard with you,” Liz added.

“How are your typing speeds?” he asked them.

“Seventy words per minute,” Jo replied.

“Forty,” Liz admitted. “I’m nobody’s secretary. But if it’s data inputting, you want, I understand what I’m looking at on the page. That’s got to be an advantage?”

The Doctor divided the pages he had to type, keeping a much larger section for himself and pointed to keyboards around the console. Jo and Liz set to work. Jo’s typing speeds were very good. She had quick, nimble fingers. Liz was slower, but she ploughed on. Both of them tried not to notice how much faster The Doctor was typing. His fingers flew across the keyboard so fast it made the eyes water to look at him. Not that either of them had time to look at him for long. The Doctor needed this data as quickly as possible. They couldn’t let him down.

It took a long time, even so. The two women began to feel anxious about the prospect of completing the process. The Doctor looked up from his work without pausing.

“Don’t panic,” he said. “Keep working steadily, and don’t make mistakes. There’s no short cut to this. We just have to keep on typing until the job is done. We’ll be ready when we’re ready. We have no reason to believe time is short. The people who survived the time anomaly are in good hands in 2012. The others... we must hope they are safe.”

“What others?” Jo asked.

“The Hypotenuse arrived in 2012. But two other buildings disappeared. We have no information, yet, about where they are. I believe that the answer lies in this data. But that is by no means certain. What is certain is that a single wrongly inputted string may lead to catastrophic failure. So work steadily and carefully and do not allow anxiety to finish the job make you less accurate.”

They took his words to heart and got on with the job steadily, wondering slightly what it was that they were creating with these strings of data, and would it really work? The Doctor, at least, seemed convinced that it would.

Liz fully believed that he was right. She was a scientist. She put her faith in formulas and data strings every day. She couldn’t see quite so clearly from the raw code she was typing just what this was going to do, but she felt she understood it.

Jo was a bit more sceptical. She put her faith in The Doctor and his hands on approach to every problem that confronted him. She didn’t understand anything that they were doing just now and she didn’t understand how it was going to help.

But The Doctor did, so that was good enough for her.

“Finished,” Jo said at last. Liz stood back from her keyboard a few moments later. The Doctor stopped typing quite so rapidly and carefully joined the three files together. Then he ran the raw data through a compiler programme and was satisfied that it was accurate.

“I’m going to run a dummy test,” he said. “Stand clear of the console. I can’t be absolutely sure what it might do.”

The two women did as he said. The Doctor pressed a final key and the console room swirled around them for twenty seconds before he reached and turned it off again.

“Well?” Jo asked. “That all looked very psychedelic. Top of the Pops would kill for that special effect. But did it do anything?”

“Yes, it did,” The Doctor replied. “It moved the whole console room, including us, forward in time twelve minutes. You didn’t even notice. Twelve minutes isn’t long enough to register in your minds. But take my word for it, we did it. Now we need to get the Captain in here and we can get on with the job.”

He went to the door and opened it. He stepped out and looked around in surprise. He stepped back into the TARDIS again and looked at the temporal clock. He stepped back out again. This time Liz and Jo followed him.

“It’s dark,” Jo said, feeling a little as if she was stating the obvious. Actually it wasn’t as dark as it should be. There were huge floodlights on the place where the missing buildings ought to be while the whole area had been screened off by the army who maintained a large and overt presence. But it was clearly night time.

“Doctor!” The Brigadier rushed up to him, followed by Benton and Captain Magambo. “At last. We’ve been waiting so long. We knocked, but there was no answer. And, of course, nobody can open the TARDIS except you. But what on Earth...”

“Twelve hours?” Liz and Jo chorused. “Doctor! Twelve hours. You said twelve minutes.”

“Oh, dear,” he murmured and stepped back into the TARDIS. The door closed behind him. Liz and Jo gave the same exasperated cry as they realised that they had been locked out. But there was nothing anyone could do until The Doctor re-emerged several minutes later.

“My fault,” he admitted with a bashful expression. “I got a decimal point in the wrong place. That’s why we moved twelve hours in time, not twelve minutes. All sorted out now, though. And we’re ready to get everything back the way it should be. Just a few things I need to know. Captain Magambo... may I have a private word with you?”

He took her aside for a few minutes. Then he thanked her for the information he gave her and took Liz aside instead. He spoke to her quickly and then wrote a note out on a sheet of U.N.I.T headed notepaper and gave it to her. She looked at it and then carefully put it into her pocket.

It all seemed like very peculiar preparations for the huge scientific endeavour that was imminent, but it must have made sense to The Doctor, at least. He then asked the Brigadier to have the TARDIS moved to the centre of the triangle between the three missing buildings with the door facing towards the Hypotenuse. He stepped back into the TARDIS and warned everyone else to stand back.

There was a whirring sound as the TARDIS built up power to the wormhole generator. Then an actinic blue light emerged from the TARDIS door, widening out like a funnel that focussed on the empty Hypotenuse. The sound grew louder and the ground vibrated slightly as the funnel widened further to take in the whole of the foundations.

Then the missing building began to appear within the funnel. At first it was a mere ghost of itself, nothing but highlights and lowlights as if the building had been rubbed out of a picture to leave only its light and shadows. Then it began to look more substantial. At last, lights came on inside the windows as the electricity was reconnected. The funnel faded as The Doctor switched off the machine.

“Is everyone ok?” Jo asked. “The people... are they alive?”

The question was answered almost immediately. Liz Shaw ran forwards as people began to pour out of the doors. She fought her way through them until she was inside the Hypotenuse.

“Where is she going?” the Brigadier asked. “It might not be safe.”

“It won’t be unless she does what I asked her to do. Professor Anders was working on the third floor. It was his project that caused the problem. But he was on the list of casualties. I’ve sent Liz to turn his machine off and stabilise the time anomaly. If I’m right, that will sort out the rest of the problems.”

U.N.I.T personnel looked after the confused victims who came out of the building. But for everyone else, there was nothing to do but wait until Liz Shaw stepped back out into the floodlit triangle. As she did so, there was another whirring sound, but this time it wasn’t’ coming from the TARDIS. Everyone turned to see the other two buildings begin to rematerialise exactly where they ought to be.

The buildings were intact. But they had problems. The south building had a pterodactyl on the roof that squawked angrily and swooped down, causing everyone to scatter in panic. A group of U.N.I.T men took aim with their rifles, but The Doctor ordered them to hold their fire.

“Get tranquiliser guns,” he said. “Bring it down alive. Don’t let it get hurt. I’ll return it to its proper place and time later.”

The other building was in much worse difficulty. It looked as if it was on fire. Again, U.N.I.T people rose to the occasion and an army Green Goddess fire engine that had been on standby was pressed into service. Jo and Liz watched in surprise as they pulled burning stacks of straw out of the foyer and doused them down.

“I’ve got a feeling they landed in the middle ages,” The Doctor said. “The people of pre-industrial Cambridge must have taken it as the work of the devil and tried to destroy it.” He looked relieved as people started to emerge, helped by the U.N.I.T men. Some were overcome by the smoke, but nobody seemed to be seriously injured.

“So the two smaller buildings were pulled back in time and the bigger one thrust forward,” Jo asked. “Is that what happened?”

“Yes,” The Doctor replied. “Simple physics – action and reaction. The force that pushed the Hypotenuse forward rebounded on the other two buildings, one receiving a bigger shove and going right back to the Jurassic age, the other getting stuck in an age of superstition and fear. Both had a lucky escape. Once Liz turned off the machine they were pulled right back here.

“We’ve lost some good people,” Liz reminded him. “We didn’t get off scot free.”

“I know,” The Doctor sighed. “And I’m sorry about that. There was nothing anyone could have done.”

“Except tell the people in 2012 what to do,” Captain Magambo said. “It was you... wasn’t it? You... in that time, still working here. You set off the alarms that got everyone out.”

“The Doctor told me to,” she replied. “It’s here, on this note. He told me to do two things on the exact date and time in 2012. I had to get all the people out. And then, twelve hours later, when we were ready to go, I had to get everyone who came with the building back into it again, standing as close to where they were when they arrived as possible. I suppose I must have done both those things. Or I will do them... eventually.”

“You are the one common denominator in both 1972 and 2012, Liz,” The Doctor told her. “You hold everyone’s fate in your hands. But when the time comes, I have absolute confidence that you’ll do it.”

“Of course,” Jo said. “She had to do it. Because if she didn’t, and the building didn’t come back, then there wouldn’t have been a building there for it to materialise into... because it would have disappeared in 1972. And if there hadn’t been a building there...”

Jo gave up.

“There was nothing I could do about the people who died,” The Doctor said. “That was already a fixed event. I’m sorry about that, Liz. I want you and your colleagues to know that. The only thing I could do was make sure you got everyone out of the building in 2012 and prevent other deaths.”

“I understand, Doctor,” she assured him.

“Well,” he said. “That’s that. Come on, Jo. We’ve got a couple of stops to make in the TARDIS.”

“What stops?” she asked.

“The Jurassic era with the pterodactyl,” he reminded her. “And we need to take Captain Magambo back to her own time. I really don’t think she wants to stay here. I’ve never seen a female member of U.N.I.T do anything but filing and tea-making. Liz, do you want to join us? You never got to travel in the TARDIS when you worked with me. You deserve a treat.”

Liz looked at the TARDIS dubiously.

“I can get you right back here,” he promised. “The TARDIS is picking up residual energy from this temporal focus and the locations where the three buildings ended up. I can follow them like a breadcrumb trail and get you back here in five minutes.”

Liz looked at Jo who shrugged and grinned.

“You’d better be right, Doctor,” she told him. “Five minutes, no later.” She stepped into the TARDIS with Jo. The Doctor told Captain Magambo she had a lift home. She said a surprisingly emotional goodbye to the Brigadier and received his respectful salute, then followed The Doctor to the TARDIS. The Brigadier and Benton watched it dematerialise.

Five minutes later it rematerialised in the same spot. Liz and Jo stepped out first, laughing conspiratorially. The Doctor followed them. He looked bemused and a little embarrassed.

“I would rather have faced a family of irate pterodactyls,” he said. “Honestly, that... I have never... never... had a grown man tell me he loves me before. That was...”

“Doctor?” The Brigadier looked at him curiously.

“It’s all right,” Jo said, trying not to break out laughing again. “The scientist in 2012, Professor Taylor... apparently he’s a big fan of The Doctor. He’s got pictures of him in ALL his different faces, apparently. And his ambition is to meet them all.”

“He was quite effusive,” Liz added.

“The Doctor needs a cup of tea and a sit down to recover from the shock,” Jo added before another burst of laughter enveloped her and she couldn't say anything else.

“Well, at least you came back here on time,” The Brigadier noted. “Come on, Doctor. A cup of British Army tea is the very least we can do for you!”