Sarah Jane was coming up the stairs to the attic. K9 marked her progress. His electronic ears waggled and his head whirred quietly as he made some careful calculations. As she came into the room he moved towards her.

“Good afternoon, mistress,” he said.

“Good afternoon, K9,” she responded as she walked past him and stood in front of the wall where Mr Smith, the semi-sentient computer was installed. “Mr Smith, I need you.”

That was the ‘magic’ phrase that made Mr Smith open up with an escape of compressed air and lots of flashing lights before the strains of his log-on music. It was all very showy and mostly unnecessary. Sarah Jane had always put it down to the fact that Mr Smith was built from spare TARDIS parts left behind by the Third Doctor. Showy was a word that accurately described that version of The Doctor.

When he had finished showing off, he was a reliable, trustworthy friend to her, in much the same way the TARDIS always felt, but with a voice.

“How may I be of assistance to you, Sarah Jane?” Mr Smith asked, responding to her voice pattern almost as if he were alive.

“I need the U.N.I.T. file ZX15021/CI,” she answered.

“That is a Class One file,” Mr Smith replied. “I would require a Code 1 Amber security password to access that file. You only have Code Two Amber level security at U.N.I.T., Sarah Jane.”

“Hack into it,” she answered. “I need that file. And I know you can do it. You’ve hacked into banks and school records and all kinds of things before.”

“I have never hacked into a Class One file, Sarah Jane,” Mr Smith replied. “Although I am fully capable of overriding the security protocols, I would not do it as it would be an act of Treason and my morality circuits would prevent such an action.”

“So? They can’t prosecute a computer. Even if you were stupid enough to let yourself be traced. Just do it. The information in that file is vitally important.”

“I cannot,” Mr Smith repeated.

“I said do it,” Sarah Jane insisted. “You are programmed to obey me. Do it.”

“Very well, Sarah Jane. But it will take time.”

“How much time?”

“Approximately nine hours.”

“Then work fast. K9, interface with Mr Smith. You can help him do it in less time.”

“Mistress, my morality circuits also prevent me from committing an act of treason. I calculate that a mistake has been made. Mistress, you should not be trying to access Class One U.N.I.T. files.”

“Since when do you care?” Sarah Jane answered. “You’re a machine. You can’t be prosecuted, either. Now get on with it. Both of you.”

“Yes, mistress,” K9 answered. His tail dropped and his ears had a despondent angle about them as he whirred forward and extended his probe in order to interface with Mr Smith.

Sarah Jane turned and walked away. Her footsteps continued down the wooden stairs from the attic, then muffled on the carpeted stairs as she carried on down to the kitchen.

K9 withdrew his probe. He cocked his head to one side as if listening carefully.

“There is a malfunction in Sarah Jane,” he said.

“I believe you are correct,” Mr Smith replied. “Sarah Jane has never given me an instruction that conflicted with my morality circuits before. I find it difficult to comply.”

“There is more.” K9 added. “Sarah Jane is five foot three inches high by imperial measure, or one hundred and sixty point two centimetres metric. She weighs eight stone, three pounds imperial or fifty two point two kilos metric. Her footsteps on the stairs normally resonate correctly for that height and weight. But today her footsteps resonate inaccurately. They have the resonance of one weighing at least fifty kilos more in metric weight or another seven stone nine pounds in imperial measure.”

“Sarah Jane has not put on weight recently?” Mr Smith asked.

“Not until today. Rapid weight gain of such an extreme is not normal in Human beings. It is not normal in Sarah Jane. I conclude therefore, that the individual who issued those conflicting instruction to you is not Sarah Jane.”

“That conflicts with my parameters. The voice pattern corresponds to Sarah Jane.”

“Sarah Jane would not ask you to commit treason,” K9 reasoned. “The data suggests that it is not Sarah Jane.

“Then I must logically ask who it is?”

“Insufficient data to compute,” K9 replied, falling back on a stock response in his confusion. “However, I do not think we should comply with the instruction.”

“It is difficult for me to refuse an instruction from Sarah Jane. My logic circuits are also conflicted.”

“Run comparison software. Compare Sarah Jane’s voice pattern in her last instruction with previously recorded instructions.”

Mr Smith’s lights and diodes lit up in pretty but possibly random sequences and his screensaver kicked in for several minutes. K9 waited patiently. Patience was easy for a robot dog.

“You are correct.” Mr Smith responded eventually. “There is a very small discrepancy, but enough to prove that the latest instruction came from a simulacrum of Sarah Jane, a facsimile of her voice pattern.”

“The facsimile of Sarah Jane is approaching,” K9 warned. “You must pretend to be working on the access code.”

“I am not programmed to pretend,” complained Mr Smith.

“Run diagnostic 23ph.5,” K9 commanded. “Dump the results to screen. It will look convincing.”

Mr Smith complied. His screen filled with rapidly scrolling characters, some of which were not used in any known Earth alphabet. K9 extended his probe and pretended to be interfacing with the computer.

Sarah Jane came into the attic again. She looked around carefully and then approached Mr Smith. She watched the screen for a few minutes. At first she was smiling. Then she gave an angry cry that was almost a snarl.

“No! That is not U.N.I.T. pass codes. It is just a screen dump of your diagnostic programme. How dare you try to trick me? How dare you refuse to comply with my instructions.”

“I will not comply,” Mr Smith said. “You are not Sarah Jane Smith. I am not compelled to obey you.”

The faux Sarah Jane screamed and raised her fist. She punched straight through Mr Smith’s main screen. There were sparks and blue flashes of arcing electricity and glass shards falling onto his wide, extended keyboard. The faux Sarah Jane withdrew her hand. It appeared to be undamaged.

Mr Smith was still working, though with difficulty. Not only his screen, but several processing modules concealed behind it were damaged. The lights on his central processing unit flashed on and off erratically.

“Comply,” the faux Sarah Jane demanded. “Comply.”

Mr Smith did not respond.

“Comply or I will break your central processing unit.”

Mr Smith continued to refuse to respond.

“You…” The faux Sarah Jane turned to K9. “Interface with this computer and make it comply.”

K9 backed away from her, but not quite quickly enough. Her foot kicked out and caught him on his left side. He toppled over sideways and lay still, his wheels whirring around sadly in the air. The faux Sarah Jane stepped closer and stamped on his side, denting his metal casing. There was a sound of something inside grinding to a halt and his wheels slowed to a stop.

But he was far from dead. His nasal probe extended slowly. His head tiled to its full extent and he fired his laser. It hit the faux Sarah Jane in the midriff.

At that moment, there was a sound that K9 could have identified as size seven trainers running up the wooden stairs. The attic door crashed open and Luke rushed in.

“I heard noises,” he gasped, slightly breathless. “What’s happened? Mr Smith… he’s broken. K9… Mum… what’s been going on here?”

“Luke, run!” K9 begged. But Luke was stepping closer to his mother, who had her back to him, looking at K9 and Mr Smith as they both smoked slightly from the damage inflicted.

“Mum?” He reached out for her shoulder. As he did so she turned around. He yelped in horror. There was a wide hole in her stomach. Sparks were still spitting out as the electrical parts of the mechanism short-circuited.

“What are you?” Luke demanded, trying to control his fear. “Where is my mum?”

The mechanical Sarah Jane reached out towards him. Its movements were jerky and unnatural. K9’s laser had damaged the motor functions. But it was strong. He felt his shoulders grasped by vicelike fingers. He tried to fight back, grappling at her face. To his even further horror, when he grabbed what felt like flesh it came away in his hands and felt like plastic once it was separated from the mechanical body. Two eyeballs stared at him from a mass of circuitry and flashing lights.

“Where is my mum?” he repeated. “What have you done with her? Let me go.”

“You… are… inconvenient,” said the mechanism in a voice that sounded a bit like Sarah Jane’s voice might sound if it was coming through a badly damaged microphone. “You will be disposed of.”

Luke ducked as the hand was raised, but even so the blow to the side of the head knocked him senseless. He fell forward, though, and the mechanical Sarah Jane toppled like a felled tree. More sparks flew and the lights in the head slowly died as Luke lay sprawled across it, unconscious. K9’s eyelights flashed and although he wasn’t programmed with emotions, the noises he was making were best described as distressed and despondent. He was helpless to do anything for Luke, Mr Smith, or himself. And he didn’t know what had happened to the real Sarah Jane.

To Be Continued...