I originally posted this in the Sherlock section, but then I reasoned that it wasn't fair to make people who enjoy this crossover sift through SO many Sherlock fics to find this kind of story. So, here you go.

Disclaimer: None of the characters in the following work belong to me, with the exception of OCs. They are the property of Steven Moffat, Mark Gatiss, Sir Arthur Conan Doyle and Gaston Leroux (even if the original characters are in the public domain. Give credit where credit is due).


Chapter 1: Paper Trail

When he heard the frantic rustle of papers as he opened the door, John felt his gut plummet to his feet. He closed his eyes. Oh, God, please let it not be as bad as he imagined it right now.

With a mental groan that echoed the aging hinges, John pushed the door the rest of the way open. It could have been worse. Morning sunlight illuminated the mess of newspapers like it were a blanket of snow. The pile concentrated itself around the table in the middle of the room. It still looked like they'd been hit by a paper hurricane, but he could remember one incident where the whole floor had been lined with paper for the sake of an experiment involving sulphuric acid. Sherlock needed to test how quickly a man could transport an open container of it across the room while keeping spill to a minimum. Sherlock had the foresight, for once, to avoid damaging Mrs Hudson's floor as best he could.

The papers seemed to serve not nearly as useful a purpose this time. The tall, curly-haired man responsible for the hodgepodge of sheets sat at the table, laptop open but eyes pinned on an immense pile of clippings which he appeared to be sorting, and then discarding, without any thought as to where the paper landed. A few pieces found their way into a neater pile next to the laptop. John deduced that the clippings held some importance. He couldn't guess the subject of interest nor why Sherlock hadn't bought a scanner to upload clippings to his computer. It would at least keep things in better order in their living space, and it would probably facilitate the detective's task.

John sighed and stepped across the threshold, then closed the door behind him with care. "Has something come up? Or are you looking at old cases out of nostalgia and boredom?"

"Did you get the shopping?" Sherlock did not deter from his task, not even to peek at his flatmate.

"Yes," John grumbled. Sherlock's habit of deferring his questions didn't bother John as much as it did a little over a year ago, when he first moved to 221B Baker Street. Not quite as much. John sighed gruffly and headed into the kitchen, hefting the plastic bag of much-needed food.

"A little of both, but your first guess was closer," called Sherlock as John placed the two bags on the counter top. "I need a second opinion."

John extracted a few packets of pre-made dinners from one bag. "Really?" he asked, almost missing the request as he opened the fridge and threw a puzzled look over the collection of jars and vials filled with a colourful array of liquids. They were all labelled with strange symbols and acronyms John couldn't decipher. While his curiosity was mildly piqued, he figured it better not to ask what they were for. One of them contained a bright, translucent yellow substance that looked like urine. John wrinkled his nose. It was still better than a severed head or fingers.

"Look at these for me and tell me what you think." John looked back to see Sherlock waving a bundle of clippings in one hand and smiling at him. Ah, yes, the smile he often used to persuade people to do things for him, which was effective most of the time. Either that or it annoyed the intended target. Right now the effect was mixed.

"Just let me take care of the shopping first," said John. Not like Sherlock could have helped or anything. But what did he expect? He kept unpacking and stashing cans of beans and soup, frozen bags of pasta and a case of beer (he would need it in the near future) as quickly as possible.

Sherlock dropped the smile. "Fine. Just hurry. By the way, the scale is broken, so stop worrying. You've only gained three pounds."

John paused as he started unloading the second bag, his hand touching the cardboard carton of milk. He whipped a startled look at Sherlock. "What?"

"The milk carton is red instead of green – you bought skimmed instead of semi-skimmed. You wouldn't normally worry about your weight unless you thought you gained an excessive amount." Sherlock rattled off his deduction in a dry, rapid-fire way that John knew belied his childish enjoyment.

The doctor let out a short, incredulous laugh. "All right. Now the only mystery is how the scale broke in the first place."

"It's no mystery," said Sherlock, turning back to the laptop screen. "I broke it. By accident, of course. A weight-distribution experiment. Didn't go quite as expected." A hesitant pause. "Sorry I forgot to mention it."

"Or replace it," John remarked under his breath. But at least his friend apologised, which was miraculous by itself. He finished putting everything away, once again facing the mysterious vials in the fridge, and again fighting the urge to enquire about their purpose.

Even after a year, Sherlock could still catch him by surprise with uncanny and unwarranted observations like that. Not to mention the unorthodox experiments that popped up out of nowhere throughout the flat. John continued to experience a measure of dread every time he opened the fridge. And who could blame him? He had encountered several nasty surprises, a severed head being just one of many.

When he completed his task, John came back to the den and saw Sherlock still holding the newspaper clips in his right hand, though his eyes were practically married to the computer screen. John reached for the clippings. To his renewed shock, Sherlock snapped them away to reach for a copy of The Guardian on the table. He then handed the whole lot to John without looking at him. "Near the bottom. The one circled in red."

John spent the ten minutes going through his assigned reading material. The circled article from The Guardian, dated yesterday, ran with the title: "Baghdad prison break-in, 2 casualties". Just two casualties? That seemed oddly low. The article explained how a major drug cartel in Iraq organized a break-in to free several of its members, many of whom faced capital punishment. It'd been an unprecedented success. When the authorities looked into how it was done, they found that the entire security network had been compromised with an unidentified code-scrambling device. It self-destructed after fulfilling its purpose.

Reading the account raised the hairs on John's neck and arms. A device that could shut down an entire prison security system was the stuff of Bond films. Such a weapon – that's exactly what it was, even if it was non-lethal – shouldn't exist in real life.

After digesting the first article, John reviewed the clippings. The titles ran:

"Puzzling burglary at the Louvre"

"Chemical weapons disappear from German laboratory"

"UFO sightings in the Ukraine on the rise"

Sherlock had written in the respective dates of the articles with the same red pen; the long-dried ink suggested he had done so at the time he filed them. The art burglary story took place last year, the chemical weapons theft three years ago, and the UFO sightings back in 2005. The stories with the robberies involved high-tech wizardry of some kind that local authorities couldn't explain. In the last article, witnesses described the UFOs as resembling missiles or rockets, but no government laid claim to the alleged weapons.

John was nearing the end of the UFO article a second time when Sherlock said, "Well? What do you think?"

He was testing him again. John leaned back in his comfy chair, the Union Jack pillow nestled behind his head, as he gathered his thoughts. "Well, on the surface they don't seem to share much in common. They all took place in different parts of the world, and the crimes . . . well, the incidents are different in nature."

Sherlock nodded and kept tapping at the keyboard. "But?"

"But . . ." John glanced over the articles again and puckered his lips. ". . . they all have something to do with complex technology. Illicit complex technology."

"Good. Anything else?"

John scratched the back of his neck. His brain worked at full throttle. "I suppose they could be linked by the people who provided the technology, although it'd be a remarkable coincidence."

"Remarkable," interrupted Sherlock, "but not impossible. Keep going."

Suddenly the doctor remembered a question he'd wanted to ask. "Do we know if any of these past cases were solved?"

"As far as my sources indicate, the technological mysteries are still open."

"All right. Then the culprit or culprits are still at large. So if they were responsible for these past cases, they could be responsible for this prison break-in."

"Very good, John. You are scintillating today." Sherlock turned around in his chair and flashed John another grin. "I told you your deduction skills would improve with practice."

As flattered as he was tempted to feel, John just chuckled doubtfully. "I'm not sure I've deduced much. After all, I have no idea who's behind it."

"True, but it's a start. You forgot to mention that if the cases are linked, the people responsible must have international connections. That's a given. What really interests me is where this operation is based. Is it a vast network of manufacturers, or a single production source? Also, I should tell you that the UFO article was the earliest record of its kind. I have about twelve other cases that seem to bear a connection to the ones you have, but these are the most intriguing. That means this operation has only been in existence for about six or seven years."

John's brows pulled together. "But if that's so, why haven't you looked into this sooner?"

"I have." With a sudden jerk, Sherlock turned back in his chair, grabbed his laptop and stood up to make two long strides to reach John's chair. He shoved the machine onto the doctor's lap. John saw Sherlock's blog on the screen at an entry for the 21st of April, 2008. It read:

The missing weapons in Germany resulted from the implementation of a code-descrambling device that allowed an agent of the Red Hand Defenders to infiltrate the main laboratory and confiscate several toxic chemical compounds. The agent was identified, found and arrested thanks to the peculiar chemical residue on the laboratory floor, which was later found on a pair of boots left by the agent in front of the door to his hotel room. Chemical compounds remain missing; the agent confessed that they were disguised with an artificial substance designed to temporarily alter their scent and texture. Agent was unable to disclose the original provider of the decrypting device and the artificial substance.

"That's it?" John wasn't sure whether to laugh or blush at the brevity of Sherlock's entry, so scant and dry compared to his own narratives. John didn't consider his writing at all flowery or overly loquacious – military training had instilled in him the value of straightforward language to convey a point. But he still managed to draft entries several paragraphs long in order to capture the drama of detective work. That was what made the cases memorable for him.

He shouldn't have been surprised, though, and he wished he had thought before speaking. Sherlock stared at him disapprovingly. "What do you mean, 'that's it'? You don't like that I don't embellish my accounts with pointless descriptions of where I ate or what my particular conversations with witnesses and suspects entailed? I focus on what's important, John: the facts. They're what I build everything on. Without them, deduction would be impossible."

"All right, I get it. So you half-solved the case."

"Yes." Sherlock's eyebrow twitched a bit and his eyes narrowed. John smiled. Seeing Sherlock annoyed reassured and amused him. It made the detective a touch more human. "I couldn't glean any more information from the man. The German authorities wanted to deport him back to Ireland straight away. They also found the stolen chemicals in a man's suitcase that was switched to a plane heading for Ulster. Once that loose end was tied up, they were satisfied and considered the case closed." He actually started to grind his teeth. "I haven't been called in for any of the other related cases. Sometimes I wonder if it's the doing of the people behind this."

"I think that's what they call paranoia," remarked John with a well-meaning grin. In Sherlock's self-made profession, however, paranoia was not necessarily uncalled for. "Isn't it possible that these cases aren't related at all? There's enough room for coincidence."

Sherlock straightened to his full height and sighed. "That may be. If so, I'll be sorely disappointed. The monotony of ordinary existence is grating away at my mind again."

This statement nearly brought John to his feet as well. "We just solved a case last week!"

"The thrill of solving your garden-variety blackmailing case can only linger for so long!" The frustrated tone of fatal boredom had crept into Sherlock's voice. He reclaimed his computer and walked to the sofa on the opposite side of the room. More like dragged his feet, except when he stepped up onto the table. Even then he made his gait appear laboured. He plopped down on his back, laptop still in hand.

Try as he might, John still couldn't completely understand his friend. Here the man had been mere minutes before furiously throwing papers all over the place and searching the Internet for possible connections between these odds mysteries. Now he was on the sofa, as if he'd been there all day, the light of the screen casting shadows along the ridges of his angular face and making his complexion look even paler than usual. Sherlock's moods could change so quickly it was a wonder John didn't get whiplash.

Their only hope was to pick up the conversation again. "Well," John said, "why these mysteries, then? Why bother reviewing them if no one is doing anything about them?"

"With nothing else to do, I have to be prepared for a windfall." Sherlock took a second to straighten out his jacket with one hand while balancing the computer on his chest. "Besides, I thought I should run it by you to make sure I wasn't imaging connections." To ensure that John wasn't gawking or giggling, he threatened him with a pointed look. "That can happen from time to time."

John gave in to another smile. A brief silence followed, accompanied by the occasional tap on the keyboard. Maybe they could go to an exhibit or something. It wasn't a murder or a break-in, but museum exhibits could hold Sherlock's attention long enough with the appropriate subject matter. John thought about pulling out his own laptop to do a quick search of what was on in the city.

As he stood, Sherlock's mobile rang on the table.

The laptop flew out of Sherlock's hands to the other end of the sofa. The detective bounded off the piece of furniture, cleared the table, and snatched the phone half a second after he landed on the ground. "Sherlock Holmes," he answered calmly. John took some deep breaths and put his hand to his chest, just to make sure his heart was still beating.

"Where?" asked Sherlock. After a few seconds his eyebrows knotted together. "A mugging? But . . . ah. I see. All right, then. Give me ten minutes." He clicked the phone off and looked up John. The old spark returned to his eyes. "Lestrade. Stacey Street. Shall we?"

John blinked and lowered his hand. "Did you say 'mugging'? Why would the police need you for a mugging?"

A half-smirk graced Sherlock Holmes' lips. "Because it's the best kind of mugging: one that isn't really a mugging, but made to look like one." Quicker than John could blink again, Sherlock tucked the phone into his jacket and shot for the coat hanger in the kitchen to grab both his and his flatmate's jackets, despite the fact it was late May. "We can put aside our mystery techno-wiz for today. I'm sure he's in no hurry to be caught. And, with any luck, he might pull another stunt after we finish this case."

"For God's sake, Sherlock, one mystery at a time!" John tried to pull on his jacket as fast as Sherlock put on his and tied the scarf around his throat. "You act as if you already have this new one in the bag. We haven't even spoken to the victim yet."

Sherlock furrowed his brow. "Why would we do that?"

John returned the expression. "You said it was a mugging. One-on-one robbery."

The taller man squinted at his friend for a moment. Then his face opened up with comprehension. "Oh! Sorry, I meant a murder as a result of a mugging. I thought I made that clear."

Again, the hairs on John's neck stood up. "Oh," he uttered, then cleared his throat. "Well, then, I guess trying to talk to a corpse won't do us much good, will it?"

"You know my methods, John," said Sherlock as he headed for the door while grinning smugly. "Those who said 'dead men tell no tales' had no eye for observation."

John said nothing in response, but in his mind he pointed out that pirates probably have little use for deductive reasoning.