"Jenny, where is Strax?" Madam Vastra asked Jenny impatiently. "It isn't his evening off, yet he is nowhere to be found."

"He took this evening off instead of his usual Sunday afternoon," Jenny answered. "He said he had a social engagement."

"I didn't think either of those last two words were in his vocabulary," Madam opined.

"Me neither," Jenny concurred. "But he asked me to iron his shirt this afternoon, and there was an odd smell in his room when I went to hang it up."

"'An odd smell'?" If Silurian women had eyebrows, Madam's would have been raised. As it was she conveyed her scepticism with her voice.

"Strange for Strax, that is," Jenny confirmed. "It was cologne."

"Cologne?" Madam was even more puzzled. "What would Strax want with cologne and where could he have gone where it might be worn?"

Jenny shrugged. It was a mystery she had not made a huge effort to uncover. She was far more interested in finding out where she and Madam were going on a Wednesday evening. She had been told to dress respectably and wrap up for a cold night.

"Never mind. Be a dear and go fetch a hansom," Madam told her wife-cum-maid with what passed for a warm smile on the lips of a cold-blooded species. Jenny did as she asked, arriving back at the house a few minutes later. Madam had donned her outdoor cloak and veil meanwhile and climbed quickly into the cab beside her.

"Where are we going, then?" Jenny asked as the snug carriage transported them through wintery London streets.

"The reading room of King's College library," Madam replied. "To listen to a lecture with magic lantern slides on the topic of "Devon and Dorset ferns and their untapped medicinal properties."

Jenny thought that sounded incredibly dull and said so.

“Ferns are among the oldest plant life on this planet,” Madam told her. “They made the land green when my grandparents were young. They are quite fascinating in their own right. But even more fascinating are the humans who collect them – especially those who think there are medicinal properties to them.”

“Do you mean that there are not?” Jenny queried. “Then why is there a lecture about them?”

"I don't know, but something about this lecture makes me uneasily curious. I feel I must attend in order to ascertain the sinister plot beneath the apparently benign subject matter."

It occurred to Jenny that there was probably nothing sinister at all about the lecture, but she kept that thought to herself. Very often it was the wisest thing to do. She also kept to herself the fear that she was going to be both bored and out of her depth at this event. The venue was daunting enough for someone with her very basic education. Even ordinary public libraries were scary enough, with their shelves full of literature she knew she could never read in her lifetime. A university library was so far above her head she was already experiencing a sort of intellectual vertigo.

“This is not just a whim,” Madam told her, reading much into her silent retrospection. “Look at these.”

Jenny looked at the selection of newspaper cuttings that Madam produced from her reticule. They were a surprising collection of reports about seemingly ordinary people who had been doing peculiar things in public. A lady called Helena Barton-Smythe tried to swim in the Serpentine – naked. Another usually sane and well-adjusted lady who worked at the British Library climbed onto the roof of the said building, telling everyone that she was going to fly. A booking clerk from Victoria Station turned up for work wearing his mother’s best Sunday dress and hat.

“My initial investigation links all of these people to the hobby of pteridomania.”

“I’m not even going to pretend I know what that means,” Jenny responded.

“It is the Latin term for fern collecting,” Madam explained. “Usually a perfectly respectable way of getting some healthy fresh air in mixed company, but the addition of ‘medicinal purposes’ to the subject of this lecture makes me suspicious.”

When they arrived at Kings College it was everything Jenny had feared. The corridors and stairways were lined with busts of great writers mounted upon pedestals and terrifyingly expensive paintings adorned the walls. The reading room continued the theme with yet more literary giants – all of them men, Jenny noticed – looking down upon the educationally inferior with alabaster sneers.

She and Madam found seats near the back of the auditorium as it rapidly filled. Jenny observed that women vastly outnumbered men at this lecture despite the misogynistic venue. Most of the ladies were of Madam’s social set, well-dressed, well-spoken, possessing small libraries of their own filled with the right sort of books. A good few were upper-working class spinsters – school teachers, librarians, secretaries, with intellectual aspirations in place of love lives. A fewer still were girls of Jenny’s own social class dressed in their Sunday best – lady’s maids brought along by mistresses with hazy philanthropic notions about exposing their servants to educational and cultural opportunities.

Through the pre-lecture buzz of quiet conversation, a porter set up several glass cases containing plants on a long side table before pinning up a large white sheet of linen upon which a strong light wavered in intensity and size as a slim woman in rather mannish tweed fiddled with the focus of the magic lantern set on a table in the centre aisle. When she was satisfied she stepped forward and introduced herself to the now hushed crowd. Her name, unlikely as it might seem, was Prunicepta Margoles and she was a self-confessed and unashamed Pteridomaniac.

This admission elicited a laugh from some sectors of the audience.

“I am glad to see I am not alone in my Mania,” she responded gleefully. “There are many new faces here, too, however, and I hope my little lecture will prove of interest to both the beginner and the advanced aficionado of the humble but utterly fascinating fern.”

With that she signalled for the lights to be turned down and the lantern show began. Jenny tried her best to look interested – or at least not to fall asleep out of boredom, but she just could not care whether one fern had eight regular fronds either side of its stem and another six and seven unevenly spaced. She wasn’t interested in which season the sori – whatever they were – turned yellow and she was never going to remember all those multi-part Latin names for plants that all looked exactly the same to her.

After half an hour, the lights came up again and Miss Prunicepta Margoles beamed widely at her audience.

“All of that is the academic background,” she admitted. “But I am going to show you something tonight that will surprise you. Indeed, I invite you to participate fully in a great experiment."

As she spoke several porters moved down the aisles with trays full of white porcelain tea cups. These were freely handed out among the audience. Jenny looked into the cup passed to her. It contained hot water in which green shreds of leaves were steeped. It certainly wasn't Earl Grey, but Jenny was aware that herbal teas and infusions were popular in the afternoon tea period of many fashionable homes.

She looked at Madam who was sniffing her own cup suspiciously.

"Are we meant to drink it?" she whispered.

"I believe that is the idea," Madam answered. Around them, at Miss Margoles' instruction, everyone was trying the tea.

"Do you think we should?"

"No," Madam replied emphatically. She pretended to drink but without a drop passing her lips. Jenny carefully copied her. She noticed the smell was something like lemon and pine with a hint of hazelnut, which was not an unpleasant combination. Even so, nothing would make her taste it.

they appeared to be the only two people in the audience who exercised any such restraint. While the guinea pigs drank Miss Margoles changed the ordinary lantern slides of ferns for something altogether odd. On the linen a coloured wheel with a swirling pattern slowly span. The audience watched with rapt attention and, at first, quiet awe. Then a primly dressed middle-aged schoolmistress stood up and swayed dizzily before declaring that she could see unicorns prancing across a violet coloured meadow.

"No, it’s dancing girls," said one of the few men in the crowd. "They're wearing dresses made of very thin silk and dancing like angels. I can see every curve of their beautiful bodies as they dance and spin and toss their heads back. ..."

"Butterflies!" somebody cried with excitement. "Hundreds of beautiful butterflies."

“Blue birds,” said another.

Clearly everyone was seeing something different. The noise rose to a crescendo as everyone talked at once about their visual experience.

Madam did the Silurian equivalent of pursing her lips disapprovingly. Jenny just sat beside her and waited for something else to happen.

Slowly, the effects died away. The people calmed. They seemed to be quite aware of what happened and some of them had the decency to be embarrassed by it, but most of them were smiling happily, as if their strange delusions had been a delightful pleasure.

“Do you feel it?” asked Miss Margoles. “Do you feel how healthy you are, your mind and body liberated by the wonderful natural properties of Polypodium Anglican ? Within a few minutes of drinking the infusion your spirit is renewed and your senses heightened in a way that twelve hours sleep in a feather bed could not achieve."

For no obvious reason everyone applauded.

"Now," she continued. "As you can see, I have cuttings of Polypodium Anglican here for everyone who would like to try the health benefits of this marvellous plant for themselves. Please come forward and take one for yourselves as you leave. There are booklets on how to nurture your fern so that you may enjoy its properties every day. All absolutely free. Financial restraint should not be a bar to the health enhancing properties of Anglican ."

There was something like a small stampede as people came forward to claim their cuttings in small pots of compost and covered with individual glass covers to maintain the warm, humid environment in which ferns best flourished.

"Go and get a cutting," Madam said to Jenny. "I'm going to engage Miss Margoles in conversation. I want to know where she found this plant and how she discovered its marvellous properties."

Jenny looked at the scrum around the table and grinned. As Madam casually approached the lecturer and unashamed Pteridomaniac she pressed into the sea of bodies, elbows digging into sides as her slender form wended and wound her way to the table and selected the lushest cutting she could find. A little more elbow work extricated her again. Madam was done with her conversation by then and the two left quietly, summoning a hansom on Chancery Lane.

"Miss Margoles claims to have found the fern growing near the Dorsetshire coast last summer and to have discovered the amazing properties by accident when frond cuttings fell into a cup of Camomile tea that she was drinking in her conservatory."

Jenny waited to hear what Madam thought about that rather mundane explanation, but for now those thoughts were unforthcoming. Madam called to the driver to stop then called out peremptorily to an unlikely figure shambling along the pavement.

"Strax! What are you doing at this hour of the evening? Get into this cab at once.”

A hansom was usually meant to take two people. Three slender and already quite familiar acquaintances might still be comfortable. But a Sontaran as the third party only worked because Jenny was happy to sit on Madam's lap.

"I am waiting to hear your explanation for your absence from my service tonight," Madam told Strax.

"It was a personal matter," Strax replied, his demeanour making it plain that he wasn't going to venture any further information.

"What is that pungent smell?" Madam demanded. "It seems to emanate from you, Strax."

"It's just as I was saying," Jenny explained. "He's wearing cologne. Buckets of it, I think."

"Madam," called the hansom driver. "We are too heavy. The horse cannot be expected to pull such a load."

"We must not overwork the noble creature. Strax, you will alight and run alongside. If we are lucky the night air of London will blow away the smell before we reach Paternoster Row."

"Yes, madam," Strax replied and obediently got out of the cab. The horse moved forward at a regular pace, pulling a load that was within the guidelines of the London Hackney Horse Protection Society.

Jenny slid off Madam's lap now that there was room to sit comfortably beside her. She looked out of the window to see Strax trotting along beside the hansom. It was a comical sight. Jenny recalled Madam telling her that the Sontaran were considered a dangerously warlike race that was the scourge of the civilised universe, but it was hard to believe that with Strax as the only example of his kind.

“Where HAS he been?” Madam wondered aloud. But the mystery of Strax’s evening excursion was secondary to the greater mystery of the peculiar properties of Polypodium Anglican. It was a puzzle that kept her pre-occupied throughout the evening despite Jenny’s several attempts to take her mind off it.

“It can’t be healthy,” Madam insisted. “People seeing visions after drinking a herbal infusion… that is NOT healthy or normal. Whatever Miss Prunicepta Pteridomaniac says, it is wrong. It is the sort of thing that goes on in Limehouse opium dens, not in respectable drawing rooms.”

“Mr Sherlock Holmes is portrayed as an opium user in his drawing room in Mr Conan Doyle’s Strand Magazine stories,” Jenny ventured. Madam laughed hollowly.

“As I said, not in RESPECTABLE drawing rooms. Besides, Sherlock Holmes indulges his disgusting habit by choice. These people are being duped into trying a drug that affects the mind. And why? The samples were given away. There is no profit to be had. I tell you, Jenny, I won’t rest until I know what is beneath all of this.”

That was literally true. Jenny retired to her bedroom adjacent to Madam’s room just before midnight. She knew that her cold-blooded wife had not gone to her own room. Several times during the night she woke and looked at the open door between the two rooms and knew the other bed was not being used.

Madam presented herself at breakfast looking no worse for the night of activity. Her Silurian metabolism did not need the same diurnal pattern of sleep and waking that humans did. She did so mainly out of courtesy to her companions of homo sapiens race. Spending the night in her workshop conducting experiments was nothing to her.

Her work was not finished, as Jenny realised over the post-breakfast cup of Earl Grey.

“I’m afraid I must use you as a guinea pig,” Madam said apologetically as she brought Jenny into the workshop-cum-laboratory and sometimes art studio. “Neither I, nor Strax would process the substances in the same way.”

Jenny looked at the two teacups set in front of her at the table. Both contained the same kind of herbal preparation they had seen being imbibed last night at the lecture.

“One is made from the leaves of the Polypodium Anglican I have been growing for years in my own conservatory,” Madam explained. “The other is from the sample I brought from the lecture last night. In case there is any element of ‘power of suggestion’ or ‘placebo’ effect I will not tell you which one is which.”

Jenny took the cup on the left and drank half of it. The taste was slightly citrus, slightly nutty, and not unpleasant, but she couldn’t help remembering what happened last night and was fully expecting to see pink elephants racing around the room any moment.

“Polypodium Anglican is just the Latin name for a fern that grows commonly in the southern part of this island,” Madam said while she waited for anything to happen at all. “Anglican simply means ‘English’, though it is strictly speaking only found in the warmer counties such as Devon, Dorset and Cornwall. I imagine every Pteridomaniac in Britain has a sample growing in their collection. And clearly you have drunk the tea made from the ordinary, common version.”

Jenny took the other cup with trepidation. This was the one that would do things to her.

Nothing happened. She wasn’t sure whether to be disappointed or not.

“Don’t worry about it,” Madam told her. “Carry on with your daily duties, now.”

It was Thursday. That meant the laundry had to be rounded up and put in the baskets to be collected. It was a job she hated but not half as much as actually doing laundry, as her sister did back home in the East End. As she collected the bedsheets and packed them into the hampers she thanked providence for her far better situation.

Half an hour later she found herself lying on the hall floor, physically restrained by Strax, while Madam was talking in reassuring tones to the laundry delivery man and apparently paying him generous compensation for being mistaken for a fire breathing dragon and set upon by a mad woman wielding a Chinese fighting stick. Jenny turned her head and saw the ornamental wooden weapon that was usually mounted on the wall now lying just beyond her reach. She also saw the laundry basket with a stylised dragon printed on it in a bright green ink and had a flashback of the creature she thought she had seen.

"Oh dear, poor Mr Li," Jenny said as Madam closed the front door and Strax allowed her to rise from the floor. "And he's such a nice man."

"I'm afraid he thinks you're a habitual opium smoker," Madam said. "It is entirely my fault. I knew that a double strength infusion might have a delayed but far more dangerous effect. I ought to have kept a closer watch on you. But this confirms everything. Strax, the carriage. We have to visit a Pteromaniac."

"Will you be requiring blast guns or grenades for subduing this terrible maniac?" Strax asked.

"Nothing of the sort," Madam answered.

As ever when extreme violence was not required Strax did his best to hide his disappointment. As he went to hitch the horse up to the carriage and bring it to the front of the house Jenny straightened her clothes and found her weekday coat and hat.

"We're going to visit Miss Prunicepta Margoles?" she asked as the carriage turned out of Paternoster Row into the afternoon traffic of Cheapside. "About her concoction."

"Indeed, we are," Madam replied. “And she may count herself fortunate that it is I, not Scotland Yard, who is coming to see her on this occasion… or that Scotland Yard are not as well versed in forensic herbology as I am.”

Jenny smiled and considered that Scotland Yard weren’t as well versed in many things as Madam. That was why they so frequently required her assistance in complicated cases. But this time Scotland Yard didn’t even know there was a wider crime than the public lewdness and other strange but apparently random acts of uncharacteristic behaviour reported in the papers recently.

Miss Prunicepta Margoles lived in an apartment near the Brompton Oratory, in the district not quite in Kensington and not entirely Chelsea. Her door off the first floor landing was answered by a trimly dressed maid who said that her mistress was not at home to visitors, today.

“Tell your mistress to make herself at home to me, or to the police. It is her choice,” Madam replied with the sort of cold glare only a reptile descendent could manage. The maid hurried off to deliver the message and hurried back just as quickly to invite Madam and Jenny in. Strax came uninvited. He was not somebody a mere maid said no to. But he did wait in the hallway on Madam’s orders, just in case grenades or other means of brute force were required.

“I really must protest at this intrusion,” began Miss Prunicepta Margoles. “It is quite uncalled for.”

“Kensington or Kaol V?” Madam replied, ignoring the protest. “I should have realised last night. You were wearing a heavy duty shimmer cloak, of course. The disguise was perfect. But those things are very uncomfortable to wear all the time. They don’t allow the skin to breathe. In your own drawing room, you allow yourself to relax. Jenny, you see it to, don’t you, my dear? The faintly perceptible blue glow, especially around the hairline and the eyes. The fingernails, too, but of course, gloves are quite acceptable day wear. Kaol is a matriarchal society which is something I quite approve of. Even Silurian males lack intellectual subtlety. They really should not be trusted with matters of State. But since when were they into the distribution of hallucinogenic drugs?”

“We made a mistake,” Miss Prunicepta replied. “I was sent here to negotiate with a great Empress who rules this planet. Instead, I found that she rules less than half of the advanced population, and in any case she is a weak, elderly woman who will die in a short time giving way to a corpulent, decadent male who is her heir apparent. True power over the British Empire lies with the men who sit in the parliament of Westminster. More fat, useless members of the weaker sex.”

“I cannot argue with your assessment of the British government,” Madam remarked. “But what does any of that have to do with Polypodium Anglican and the Pteridomaniacs?”

“It is an experiment in creating anarchy,” Miss Prunicepta replied. “Small test groups to begin with – the audiences at my Pteridomania lectures. Then when I am ready, when I have the dosage correct, I won’t waste my time persuading them to drink herbal tea. It will be put into the drinking water. The resultant anarchy will allow the Empress of Kaol to take this pathetic British Empire easily and then destroy any other opposition to our possession of this planet.”

“And you’re telling me this because?” Madam asked, surprised not only by the sheer audacity of launching a world takeover from an apartment in Kensington, but the detailed exposition of the plan.

“Because you are alien, too. You can help me enslave these pathetic humans.”

“I’m not alien,” Madam replied. “This planet belonged to my people before the humans had learnt to stand upright, and I will not have any upstart interfere with it. one day my own people will re-assert their authority over the Human race, and until then, they at least are indigenous to Earth. I will take their side against alien invasion any day.”

“Besides,” Jenny added. “We humans aren’t keen on being taken over.”

Miss Prunicepta had not been looking at Jenny. She had been dismissed as a weakling Human slave. She didn’t expect the weakling Human to knock her down with the same martial arts techniques she had unwittingly practiced on Mr Li of the Green Dragon Laundry. Nor did she expect a genuine alien dressed as a carriage driver to pin her down, again using the technique he had used on Jenny earlier.

“Permission to use personal stun grenades, madam,” Strax requested. Whether he meant against Miss Prunicepta or her maid, who had started screaming in shock just about the point when Jenny pounced and was still screaming without having taken a breath.

“Not necessary,” Madam responded. “Just hold her down for a little while longer. Jenny, please take the maid to the kitchen and make her a cup of tea – real tea, that is. Strax, let Miss Prunicepta up now, and sit her in that chair by the window. While Scotland Yard get here, she can write out her confession.”

“Confession?” Strax queried. “You don’t wish to have her dismembered?”

“Confession will be fine. She can explain how she deliberately poisoned members of the audience at her Pteridomaniac lectures causing them to have hallucinations and behave abnormally. She can admit full responsibility for all of the crimes unwittingly committed by these innocent dupes.”

“And if I don’t?” Miss Prunicepta asked with just a little bravado but with one eye on Strax’s squat but powerful figure before her.

“If you don’t, then I will let my manservant rip your head off as he so dearly wishes to do,” Madam replied. Miss Prunicepta looked her in the eye and saw the full depths of authority invested in a woman who was born two hundred million years ago.

She wrote her confession. When Scotland Yard’s men arrived the case they didn’t even know they had was already solved.

“I found a nice, quiet position for the maid in Lady Philippa Durham’s country house,” Madam Vastra said when she and Jenny were settled, later, with a nice cup of tea. “Just because her mistress was an alien with ideas above her station doesn’t mean she ought to be unemployed.”

“That was kind of you,” Jenny told her.

Madam brushed the matter aside as if it was unimportant, but Jenny appreciated her aristocratic wife’s attempt to be philanthropic towards the poorer classes.

“Speaking of Lady Philippa,” Madam added. “She was telling me about a new venture of hers to raise the cultural awareness of the servant classes. She has sponsored a ballroom dance and supper club.”

“I hope you’re not suggesting I should join it?” Jenny remarked.

“Not at all, my dear. But you’ll never guess who HAS become an avid member.”

For a moment Jenny couldn’t guess, then her eyes widened in astonishment.

“No!”

“Yes! Apparently there are a number of small, plump kitchen maids with whom he is very popular.”

“But… ballroom dancing?”

Jenny could just about imagine Strax performing a waltz. The steps in that were limited and repetitive. But then her imagination bumped straight into the minuet and suffered a concussion from which it could only recover with another cup of Earl Grey.

Still, two mysteries solved and an alien invasion averted in less than twenty-four hours wasn’t bad going.