A/N: This is the first chapter of book 3 in my Johncroft series. (Its predecessors are Promise to the Living and The Devil in Devon.) If you haven't already, I recommend that you read the first two fics, as Danger Nights features some OCs. To all those who are continuing with me in this AU: welcome back! -Deklava

P.S. Love and thanks to my beta, chasingriver.

John Watson was exhausted but happy. He and Greg Lestrade had spent the afternoon and early evening at an invigorating football match (London won), and Mycroft would be back from Prague tomorrow morning. As their cab turned onto Baker Street and stopped in front of 221B, he acknowledged that life was good.

Lestrade looked over at him. "What time does Mycroft get in tomorrow?"

"Early. Five-ish." John smiled as he took out his wallet. Sunrise arrivals invariably meant that he'd wake up in Mycroft's arms. The elder Holmes would take a chauffeured car directly from the private airport to Baker Street, let himself into the flat, and slide into John's bed, sometimes fully dressed… and sometimes not. They'd kiss, touch, and make love while daylight gradually brightened the room, relishing the rare intimacy of solitude. Their respective obligations made theirs a relationship sustained by calls, texts, and stolen time, but neither complained. They were, above all else, men who understood the concept of duty.

He couldn't wait for morning.

When he paid the cabbie and exited the vehicle with Lestrade, the first thing John heard was loud music. It wasn't coming from Sherlock's violin either. Judging by the range and volume of the clamour –pulsing bass, crashing drumbeats, reedy synthesizer riffs- either a rock concert or a block party was being held in the flat. Intermittent laughter provided an underscore.

"What the hell?" He stared up at the windows, where the curtains shivered under the force of the noise.

Lestrade's expression wavered between amusement and disbelief. "Any chance Sherlock decided to sponsor a rave and not tell you first?"

John shook his head. "Not a chance." He couldn't see Alexei being behind it either. The fourteen-year-old was staying with Sherlock and John while Mycroft was playing political chess in the Czech Republic. Like his father and uncle, Alexei had an aversion to pointless social gatherings. "I spend my time playing count the idiots," he grumbled once.

Baffled and now a little worried, John ran toward the door and nearly dropped his keys twice in his haste to unlock and open it. Once he and Lestrade were inside, the music's volume nearly sent them both staggering back into the street.

"Bloody hell!" Lestrade shouted as they both covered their ears. "The neighbours will report Mrs. Hudson for a noise disturbance."

Cringing at the thought of the landlady coming home from her Brighton vacation to a court summons, John led the way upstairs.

The two men burst into the flat, which had been an ordinary –if messy- dwelling only hours before. Right now it was doing double duty as a dance bar. Half-naked bodies snogged on the furniture and gyrated to the music. Liquor bottles, most of them empty, covered the coffee table, mantle, and kitchen table, where they infiltrated Sherlock's chemistry set.

"Hey!" a male voice yelled. A beefy teenaged boy with spikey black hair and kohl-ringed eyes was waving John's army automatic around. "Finally got the box open and look what's inside!"

John pushed through the half-somnolent bodies toward him, but Lestrade was faster. The former Detective Inspector grabbed the kid's wrist with one hand and used the other to wrest the weapon away. Then he pinpointed the source of the music- a surprisingly tiny MP3 player hooked up to boulder-sized speakers- and abruptly unplugged it, plunging the flat into silence.

"Listen up, everyone!" he bellowed as he tucked the gun into his waistband. "Party's over. Clear out- all of you."

A spotty-faced youth wearing ripped denim jumped off the sofa. "What's the deal, you old codger?" he demanded while his over-hennaed girlfriend giggled loudly.

Lestrade walked up to him. "How old are you?"

"Seventeen."

"It's your lucky day then. Because if you were eighteen, you'd be going out the window, not the door."

John couldn't tell whether it was the threat or the cold, dangerous look in Lestrade's eyes that made the kid swallow nervously and sit back down.

"I'm not going to say it again." The ex-Yarder joined John at the door. "Everyone out. Single file. If I see any of you carrying something that belongs in this flat, you'll be turned over to the police."

John found his voice. "Wait a minute. Where are Sherlock and Alexei?"

Sherlock's sultry baritone responded. "I'm here, and I believe that Alexei is still monitoring the experiment in the toilet."

John spun around. Sherlock was on the landing, carrying shopping bags loaded with wine and liquor bottles.

"Sherlock," he said, keeping his voice level only via supreme effort, "what the FUCK is going on here?"

"An experiment," Sherlock replied as he approached. "And one which your inconveniently timed arrival may have ruined, might I add."

"What?"

"Everyone out. Now," Lestrade ordered the now-silent crowd. Grumbles accompanied the creaking of sofa springs and floorboards as the kids all filed out. One girl with turquoise hair and an intelligent face said before leaving, "You'll want to check the bedrooms. Might still be people in them."

John's blood pressure rose. Lestrade said quickly, "I'll go look."

"They won't be in mine," Sherlock told him. "I locked the door."

Shaking his head, the ex-Yarder headed for John's room. When he was gone, the detective walked past John into the flat and dumped the bags on the sofa in a fit of pique.

"I just spent eighty pounds for nothing," he scowled.

John put his hands in his pocket to avoid wrapping them around his flatmate's graceful neck. "I'm still waiting for you to explain why our flat is the place to be in London tonight."

"It's for the Benning investigation."

He was referring to the latest case that the HWL (Holmes-Watson-Lestrade) detective agency had accepted. The client, a wealthy Hampstead resident, claimed that her sister's recent death had been murder, not accidental asphyxiation. Lestrade had called on some former colleagues at the Met to obtain a copy of the investigation file, which included some rather nauseating photos of vomit contents and patterns.

John was dangerously close to exploding. "What's that got to do with your letting minors into our flat and buying liquor for them?"

"We –Alexei and I- are photographing samples to compare to the evidence collected at the scene. I need more information about the digestive process and what regurgitated food looks like at various stages after being initially eaten."

John's nostrils flared. Sherlock didn't seem to notice. He actually looked pleased with himself as he continued.

"Each time someone goes into the toilet to be sick, Alexei follows them, asks when they last ate, and takes pictures."

Lestrade reappeared with a teenaged couple in tow. They were giggling and rearranging their clothing as they left the flat. "Toilet door's shut," he said. "But Alexei's in there with some kid who's being sick." Glancing at John, he commented, "I'll bet Sherlock's explanation is interesting."

"Idiotic would be a better term," John growled. Although he suspected that he knew the answer, he added, "Whose fucking idea was this?"

"It initially occurred to me when a pair of rather inebriated young girls arrived on our doorstep thinking they'd reached a different address, where a party was being hosted. One of them became ill on the pavement, and Alexei had the presence of mind to take a picture. But a single sample is not sufficient data, so I invited the young ladies to come in and have a party here, and invite their friends." Sherlock sniffed in disdain. "They proved to be more popular than their appearance warranted."

"So you bought them liquor to make them sick so you could get these 'samples'."

"I didn't pour it down their throats, John."

"What you did was illegal," Lestrade scolded.

"Mycroft would have stood down any police interference."

Mycroft's name made John think of Alexei. Needing to get as far away from Sherlock as possible before he lost it completely, he walked to the toilet door, which was still closed. Hearing whispers on the other side, he pushed it open.

A big youth who had to be at least nineteen sat on the floor, legs crossed and back braced against the wall. The toilet had been flushed, thank God, but the air was so hot and sour that John grimaced.

Alexei squatted on his heels, elbows resting on his knees and a camera clutched in one hand. "John," he greeted without looking up. "I heard you and Gregory come in. I hope the guests didn't disturb the place too much."

"Pathetic as this sounds," John said, "I'm not too surprised to see Sherlock pulling a stunt like this. But you… I'd always hoped you'd be the adult."

Alexei wasn't chagrined. "It was a perfect opportunity to collect data for that case."

The drunken youth, who was fiddling with something in his pocket, snickered. "This your dad or something?"

John glared. "No. His dad is going to have a lot more to say about this than I will."

Alexei didn't look worried. "It's for a case. He'll understand."

"Don't be so sure," Mycroft Holmes said.

Alexei's eyes widened and John spun around, heart leaping in joy despite his earlier fury.

Mycroft stood in the dim hallway, looking elegant and imposing in his tailored overcoat and teal blue three-piece suit. A solemn-faced Lestrade and a visibly uneasy Sherlock hovered behind him.

"I was able to conclude my obligations earlier than expected," he said as he approached. The light over the toilet sink shone on his face, revealing an expression that stopped John cold. "I anticipated a pleasant reunion. Instead, I found this on the stairs."

He opened his gloved fist and held it out, revealing a dirty-looking vial of white powder.

"Hey, can I have that if you don't want it?" the drunk kid slurred.

John stared down at the plastic container. Having worked with addicted soldiers, he recognized its contents immediately.

Cocaine. Concentrated destruction in a vial. And Mycroft had found it in the building where his brother, a former addict, lived. Where his son was staying. John quickly forgot his own anger as he realized that terrible memories had to be running through the man's head right now.

"It doesn't belong to anyone here, Mycroft, you know that," he said gently. "But it's been a bit mad here tonight. Come on, let's go into the living room and Sherlock and Alexei will explain-"

But Mycroft wasn't listening. His eyes rolled back in his head just before the British government fell.