"Men were deceivers ever
One foot in sea and one on shore
To one thing constant never,"
- William Shakespeare

Chapter I

Sherlock was only nine years old when he began to suspect his life would be unbearably dull. It was a simple question of mathematics. Mermaids lived, on average, between five and seven hundred years. Seven hundred years, swimming the same paths, having the same conversations, occasionally composing a new song to break the monotony. Sherlock felt nauseous just thinking about it.

His teachers told him that he'd be happier if he made more of an effort to make friends. A lot of people wanted to be friends with Sherlock. He was royalty, after all. But talking to other children around him only seemed to make the boredom yawn wider in his chest. All they wanted to do was shine their tails and brush their hair and discuss who was the most beautiful or who had the best singing voice (a pointless exercise as the answer to both questions was, quite clearly, Sherlock). Sherlock got into the habit of swimming off and watching the fish instead. They were even stupider than mermaids, their brains slow and basic in the extreme, but there was a kind of satisfaction in puzzling out the rhythms of their lives, the patterns in which they swam, how they lived and died, ate and were eaten. On weekends he swam further afield, and found himself a pod of dolphins to swim with. Dolphins were quicker, smarter, more cunning than fish but they always wanted to play the same games and Sherlock got bored again.

By the time he was ten years old, Sherlock had charted every square mile of the Inner Queendom, observed and noted the movement and behaviour of every different species within it. When he came to the realisation that there really wasn't any new to see, not anything at all, Sherlock curled up on a knoll of seaweed and cried. That was where his brother Mycroft found him some hours later.

Mycroft looked down at his little brother and sighed. Mycroft sighed a lot, it was his way of reminding everyone how much more clever and important and responsible he was than anyone else. He especially liked to do it when speaking to Sherlock.

"Go away, Mycroft." Sherlock said, as imperiously as he could manage with a face still flushed from sobbing.

Mycroft didn't reply to this, merely flicked his long tail and drifted over so he could float by Sherlock's side."If you like I could speak to Mummy about assigning you a small role in the Governance." he said. "You are young for it but time does pass more easily when you have duties to fill it."

"You'd like that, wouldn't you?" Sherlock said. "Making me your errand boy. Well, I won't do it. It's all stupid anyway." He curled up his hands into fists, and crushed them against his eyes, hard enough that spot appeared in front of his eyes.

"I know." Mycroft said.

Sherlock looked at him in surprise. Usually Mycroft couldn't stop talking about how Great and Important and Worthy his work for the Queendom was.

"When I was your age, I felt the same way." Mycroft said. "Most people aren't as clever as we are."

Sherlock snorted at the understatement.

"It does get easier, as you grow older. You find interests in the world, in your work…"

"Really?"

Mycroft smiled, thinly. "Maybe Governance isn't your destiny. But you will find something, Sherlock."

"Maybe I'll just go and get myself eaten by a shark."

Mycroft glanced at him, frowning. "That isn't amusing."

"I wasn't joking."

Mycroft turned his tail lightly, flipping onto his back. He looked upwards through the water. "You know – I shouldn't…." he trailed off, frowning.

Sherlock was immediately interested. "What?"

"You have made a study of almost every species in this Queendom. Have you ever thought to look above the surface?"

"You mean gulls and albatrosses?" Sherlock asked, disappointed.

"I mean Humans." Mycroft said quietly.

Sherlock sat up.

"I thought I wasn't allowed to – "

"You aren't." said Mycroft. "You're far too young to go near the shipping lanes. But there are, there have been – Findings. Objects from the world above that came down to us, in wrecks or by accident. There are those who make quite a study of it. When I was your age I went through a phase when I was rather fascinated with it myself. "

"Will you show me?" Sherlock asked, eager in spite of himself.

Mycroft hesitated, then sighed. "You'll need a special security clearance. It's a very great responsibility. I wouldn't offer it unless I –"

But Sherlock had shot up off the ground and was turning a loop in the water grinning..

"You will let me."

"Yes, yes." Mycroft smiled at his brother's enthusiasm. "But – listen, Sherlock. I must warn you– there are dangers to the study of Humanity. You must not allow yourself to be seduced. Do not forget who you are."

Sherlock rolled his eyes. "Of course not."

"Hmm. Well, come along then, Sherlock. It's almost time for the Banquet and Mummy will be waiting."

"But will you –"

"I'll take you to the Warehouse." Mycroft promised. "Later. But first, make yourself presentable. The Ambassador will scream if you go down to dinner looking like that."

If Sentinel Lestrade had previously thought Prince Mycroft seemed a bit mad, the morning's events had confirmed the suspicion. The man had strolled in to his office that morning with a distant smile and casually announced his intention to introduce a ten year old child to the highly classified and exceedingly dangerous work of the Human Squad. If he was an ordinary person they'd be taking the man down to the Sanatorium to be evaluated.

But of course, he wasn't an ordinary person, he was a Prince, and they all had to do what they were told.

"Is he serious?" His second in command, Donovan, made a face not unlike the back end of a walrus when he passed on the news.

"It seems so. I think the kid just has a few questions – he's the curious sort. You know? We'll just give him a quick tour, chat to him for a bit. I'm sure he'll get bored and wander off after a while." Lestrade tried to sound reassuring and not at all like he thought the man who was second in command of the whole Queendom was having a nervous breakdown.

"I hope so." Donovan snarled. "I didn't sign up to be a babysitter."

"I hear that kid's pretty weird." Anderson swam over. "My cousin teaches at his school. Says he never talks to any of the other children, just wanders off and bothers the fish."

"Well, that's royalty for you." Donovan said. "Too good for anyone else."

Lestrade cleared his throat rebukingly. "Now, now."

"He has a lovely voice." Mollysa, their Remains Expert said from behind him. Lestrade tried not to jump. Mollysa was such a quiet little thing, he tended to forget she was there.
"I went to a banquet at the palace, and they had him sing. He's really – exceptional. I don't think I've ever heard anything like it."

"That could be useful, if he really does have an interest in working with Humans." Lestrade said thoughtfully.

"He is far too young for Siren training." Donovan said.

"I know," Lestrade shrugged, "No harm in planning ahead though, is there? Come on, Donovan, make nice. You never know when it might pay off."
Donovan pursed her lips.

In fact, introducing Prince Sherlock to the Human Warehouse turned out to have very little in common with babysitting and rather a lot on common with sitting an unscheduled and extremely stress inducing inspection. The young Prince had questions about everything, and fixed Lestrade's team with an icy stare when they he was not answered adequately and in full. Lestrade hadn't felt so nervous since his Advanced Human Culture assessment back when he was training to join the Guard.

"What is this?" Sherlock picked up another item from the shelves.

"Careful," hissed Donovan behind him. Lestrade shot her a glance. "Your Highness," she added grudgingly.

"We believe, some sort of weapon." Lestrade explained. "Or possibly a surgical tool."

"Hmm." Sherlock looked down his nose at it. "The latter is more likely, I'd say. Look at the rotating mechanism – it must have a very specific purpose. And while it could certainly do some damage, it is hardly something one would reach for in the heat of the moment." He held it up to the light, pale eyes glowing with interest. "Fascinating. May I keep it?"
Donovan made an irritated noise in the back of her throat.

"Of course," Lestrade said.

The Prince didn't bother to say thank you.

Lestrade was wrong about Prince Sherlock becoming bored. He very quickly seemed to make the Warehouse his second home, spending every spare hour he had wandering around the long corridors, picking out items and examining them with a ferocious interest. As they soon discovered, he had quite a gift for analysis. Donovan was almost apoplectic with fury when Sherlock took one of their oldest finds (a circular metal box, found among the clothes of a drowned mariner) apart, until he explained that he had figured out the mechanism. He gathered the disgruntled team around him and explained how a series of cogs and screws operated to keep a little stick rotating upon an axis under a glass face.
"I think it's a timekeeping device." Sherlock said, his pale face ablaze with interest. "Some way of marking events as they pass."

"How can you possibly know that?" Anderson's eyebrows were raised.

Sherlock looked back at him disbelievingly. "What is it like in your tiny little minds? Look, these are numerals, clearlyeven you would recognise them. It isn't designed to interact with its environment, it runs on its own cycle: and if you look around there are at least two other devices in this warehouse designed in the same way, even though they originate from different ships. They measure a constant, something that follows the same pattern in different places, and in different ages. And it's a practical tool, just look at the scratches on it – this has been kept close, used, constantly. What could they be measuring, what would they need to measure in this way? Humans live above the surface, they don't have the pressures of the tide around them all the time, and looking at the sun is too imprecise for complex arrangements- they had to find their own way of measuring time. With this. It's obvious."

Lestrade had to admit it was an impressive theory. Certainly more imaginative than anything any of his team of analysts could come up with. He had a feeling the same thought had struck his team, and that they were not enjoying the idea.

"He's a freak," Anderson spat out later, once Sherlock had left touting another of his supposedly classified trophies. "Have you seen that kid's face when he touches the Human objects? He practically glows. Its bordering on obscene."

"It gives me the creeps." Donovan agreed. "The gods only know where the kid'll end up. You know, he asked me about the Ithillya Rain? I told him I'd been there, that I'd seen the place the ship went down. It's the kind of thing any normal child would have nightmares about. He was excited."

"He's just curious." Lestrade said firmly. "He's still young. He'll understand the emotional aspect of what we do better, with time."

Privately, though, Lestrade did worry that the young Prince didn't display any of the healthy disgust Mermaids usually felt when dealing with Humankind. On the contrary he seemed rather dangerously enthralled with them. Lestrade worried for the boy. The more time he spent with the Prince the more it became apparent how isolated the child was. The boy had no father to speak of, no friends and his mother was too busy ruling the Queendom to attend to him. The only person who seemed to take an interest in Sherlock's development was Prince Mycroft, and his idea of care mainly seemed to involve pointing Sherlock in the direction of a dangerous hobby and letting him get on with it. It was small wonder that the kid had a warped view of what was normal.

Perhaps it was time Lestrade had a word with the boy.

"You know, your Highness." He began, swimming over to hover beside the boy as he examined a peculiar piece of carved wood. "You do have quite the gift for analysis."

"I know. Obviously." Sherlock ran his fingers over a carved S shaped hole in the wood. "What does itmean?" he muttered to himself.

"But I was wondering whether you knew why we do what we do. About the history of Mermaids and Humans."

Sherlock looked up, frowning.

"I don't know what they teach you in school."

"Not much." Sherlock said. "And it's mostly wrong anyway. I told my teacher but she wouldn't listen to me."

"Right." Lestrade said, feeling a flash of sympathy for Sherlock's teacher, whoever she might be. "Well. Humans are – as you know, we used to live side by side more or less peaceably, until a few centuries ago. We didn't have much to do with them, of course, but they didn't harm us, nor we them. But then their numbers increased and they began to pump out dirt into the seas. It became dangerous for mermaids to stray too close to the shores, because there was poison in the water. Even eating the fish from the coastlines could make you sick. And the Humans became greedy, pulling more and more fish out of the ocean, several Queendoms experienced famine. And then, there came the Black Rains – "

"I know about that."

"With all due respect, Your Highness." Lestrade said gently. "I don't think you do. I was there a couple of weeks after one of them, in the Antagondom Queendom. The water had gone black, blotted out the sun. Particles of darkness drifting down through the water, everywhere – those in the worst hit areas suffocated within minutes, others, further away, died more slowly. Some people swam to the surface only to find themselves covered with the stuff, coating their skin and blackening their hair, we couldn't get them clean…. Hundreds of mermaids had to leave their homes behind, the crops were ruined, there was famine…."

Sherlock had put down the instrument now and was listening, mouth half open.

"And then, there was Atlantium. No one even knows what happened there. There was a blast of light, a shiver in the water that mermaids felt from here, and everything within leagues of the Queendom just died. The rocks in that area still glow."

Sherlock shivered, a faint flush on his cheeks.

"I don't mean to scare you." Lestrade said kindly. "But if you work with us, it is important that you know these things."

"I'm not scared." Sherlock was pressing his fingers to his lips, obviously deep in thought. "I didn't know they possessed so much power."

"Yes, well," said Lestrade, a little unnerved. "You do need to know what you are dealing with."

All of a sudden Sherlock sprang upwards, his scrawny body pulling itself straight.

"Mycroft." He said.

"What?"

Sherlock's eyes shone with the light of a new discovery. "He's been lying to me – to you too, probably."

"I'm sorry," said Lestrade. "I don't follow."

"Never mind." Sherlock snapped. "I need to see my brother."

And he swam away without a backward glance.

Lestrade looked after him, mystified. Well. That could have gone better.

Mycroft looked at his little brother wearily. How exactly he'd managed to bypass three sets of Guards and a locked door and find his way into Mycroft's office he didn't know. He would have to re-evaluate his security measures. Again.

"I want to see the scrolls."

"What scrolls?"

"The secret scrolls." Sherlock said. "I know they exist. You wouldn't let such a rampant threat to national security exist without having more information than this. There is more – I want all the information you haven't seen fit to share it with Lestrade and his troupe of floating morons."

"It's always nice to hear that you've been making friends."

"Mycroft."

"You are ten years old. If these scrolls do exist, why on earth would I share them with you?"

"I'm almost eleven. And I will find out what they contain eventually. There will be less effort on your part and considerably less embarrassment if you let me see them now."

Mycroft fought very hard not to smile. His little brother, ten years old and already sharper and more determined than half the Queendom put together. While he wouldn't have liked it to be generally known, and certainly not by Sherlock, Mycroft loved his little brother quite inordinately. Before Sherlock had been born Mycroft had been quite alone in the world. Sherlock was the only one, apart from their mother, who had a mind like Mycroft's, bright and brilliant and utterly unable to find satisfaction in any of the banalities with which most Mermaids occupied their time.

"Very well," he said as coldly as he could manage.

Sherlock's eyes widened. "Really?"

"As you say, you'll find your way to it eventually, and I have no desire to spend the next few months fending off your attempts at espionage."

Sherlock's smile was so wide it looked like it might actually cut his face in two. Mycroft told himself he is making the right decision. He had to be.

"What is Hudson?"

"Hmm?"

Mycroft was preparing himself for a very important banquet. It was of paramount importance that he looked his best. He wound a shell bracelet around his forearm, leaning back to admire the effect. Not quite the correct shade of blue, he feared. He looked again at his collection spread out on the shelf. Perhaps the coral.

"Hudson. It's mentioned in the scrolls as a source, several times, but there's no explanation of what it is."

"Ah." Mycroft cast a glance back at his little brother, who had ensconced himself in his sleeping hammock and was watching him through narrowed eyes.

"You might as well tell me." Sherlock whined at him. "I know practically everything else."

Mycroft sighed, and wondered yet again if he ought to have allowed Sherlock's obsession to progress to this point. But then, what choice did he have? It had been the best way to forestall Sherlock from going down a worse path. At least he was spending his days in a way that might one day benefit the Queendom, instead of swimming off into the path of predators or under the helms of ships….

"Hudson isn't a what. It's a who."

Sherlock sat up at this. "A Human?"

"No." The pink torc made Mycroft's arm look uncomfortably chubby. Perhaps he should consider another diet.

Sherlock slumped slightly. "What then?"

"A merwoman. She was taken prisoner by Humans some four hundred years ago. Unpleasant business. I believe they kept her in a cage, treated her as some sort of circus exhibit. At any rate she escaped, and managed to return to her own kind. We interviewed her extensively. She is the source of much of our most reliable information about Human culture."

"She's still alive?"

"I believe so."

Sherlock sat bolt upright, his face pale. "I want to meet her."

Mycroft smiled thinly. "No doubt."

"Please, Mycroft."

Mycroft sighed heavily, and waited for a few beats, watching Sherlock's face grow taut with tension.

"First, I'm going to need you to do something for me."

"What?" Sherlock frowned suspiciously.

"Your voice coach thinks you show great promise."

"Oh." Sherlock said unenthusiastically, "That."

"I want you to undertake training to be a Siren. I have written to Ithilliya, they are sending their very best Siren to teach you."

"You've employed Irene the Adler?" It seemed even Sherlock couldn't help but sound a little impressed.

"Like I said, Sherlock, I believe you show a great deal of potential. It would be quite something for the Queendom to have a first class Siren at its disposal. It will require a great deal of commitment on your part, however. I need your assurance that you will take this seriously. It would not do to be made a fool of in front of the Ithilliyans."

Sherlock tilted his head speculatively, watching Mycroft. He was waiting to give an answer, building the tension in the room, just as Mycroft would have done. Mycroft felt a rush of pride. If Sherlock could learn to manipulate, he could do anything.

"You should wear the purple shells." Sherlock said. "Your hair is by far your finest feature. Purple brings out the subtler shades, makes it appear to shine.And its slimming." He got out of the hammock and swam towards Mycroft. Their eyes met in the mirror.

"I will work at Siren training, as diligently as you could possibly desire," Sherlock promised. "If you allow me to meet Hudson."

Mycroft smiled. "I will send you round a briefing tomorrow morning."

Sherlock nodded and drifted out of the room. Mycroft picked up the purple armlet. It did suit. Sherlock was right, as usual.