Seriously, this crossover makes sense!

Note: Everything said by Agent J is direct script from MIB2, and as such, I do not claim credit for his witty words.

A Bug in the Electrical System

When Sherlock was seven, he developed an aversion to public transportation, which may or may not have been due to the 600 foot worm that tried to eat him on a trip in New York.

Sherlock had been alone on the trip with only Mummy by his side at the time. Mycroft, his older brother, was back home with Father, finishing some sort of exam paper as an excuse to stay in good ol' England. The seven-year-old didn't know if he should call Mycroft lucky or unfortunate to have missed this unbelievable event. On one hand, Sherlock felt special witnessing something his brother had not, on the other, no one would believe him – not even Mycroft, no matter how insistently Sherlock swore on it.

Sherlock was in the tube (subway, the Americans called it) with Mummy when it occurred. One second everything was peaceful, the next, a black man came flying through the back window of the subway car.

Sherlock's eyes widened as the man got up idly, brushing off the glass shards as if it were an everyday event. No one else seemed bothered by it either.

"Transit authority, people. Please move to the forward car, we've got a bug in the electrical system," the man said, flashing a badge so quickly Sherlock couldn't even see what was on it.

No one moved.

Sherlock observed the man the best he could. He sounded calm, but he also looked nervous and urgently serious. "Yo, people-" the man yelled.

Sherlock turned to Mummy, "Should we move?" he asked her, something not sitting right with him about this whole thing. If Mycroft was here, he would know what it was.

"I'm sure it's just a prank," Mummy soothed, "Apparently they get that a lot around here."

And then giant jaws ripped apart the end of the car.

Around Sherlock, screaming tore through his eardrums as people scrambled away from the beast. The world froze around Sherlock as he stared at the impossible worm-thing contently chewing through metal, even while Mummy tugged franticly at him to drag him away. Everything Sherlock thought he knew about the world suddenly collapsed.

"Sherlock! We have to get out of here!" Mummy shrieked alongside the rest of the passengers, cursing her decision to come to the Big Apple.

Sherlock could feel the need to follow the mass in screaming and hiding, bubbling inside his rapidly beating heart. Half of his mind told him it was only the natural thing to do, while the other half chided him that Mycroft wouldn't be doing something so useless if he had been here as well. What would Mycroft do?

Sherlock allowed Mummy to continue dragging him away while he fixed his eyes on the man in the pristine black suit strolling casually behind them, throwing sarcastic sentences at their fleeing backs. "Oh, now y'all running? No, no, no, sit down; it's only a 600 foot worm."

As he seemed like the only one who knew what was going on, Sherlock figured the best course of action for them all was to follow the man's lead.

Sadly, some people were utter imbeciles.

"I'm Captain Larry Bridgewater, and I decided what happens on this train," the conductor said, completely ignorant of the giant worm who'd managed to devour more than half of the train already.

Quickly, the other man managed to put him right, much to Sherlock's amusement (or as amused as Sherlock could feel underneath his terror), before turning back to the worm and attempting to converse with it – holding it at gun point. "Don't make me do this, Jeff," the man demanded.

…Jeff?

Slowly, but surely, the worm withdrew, closing his mouth with a low whining sound. Sherlock felt enchanted by the man.

When the half chewed car arrived at 81st street, the seven-year-old tried to push past everyone else, eager to question the man about the illogical, impossible monster in the rails. With his eyes fixed so intensely on him, Sherlock picked up the wary way the man securely fixed a pair of sunglasses on his face and the way he quickly forced himself to the front to stop them all from getting off. Suddenly, Sherlock was suspicious of the man's next actions, even if all he seemed to do was reach into his suit pocket and pull out a cylindrical rod.

Sherlock wasn't sure how fast his mind was running within the next few seconds, but his deduction led him to hide under the car window unseen, with his eyes squeezed shut - If the way the man was pointing that thing at them along with the thick sunglasses the man was wearing, was any indication, Sherlock knew he shouldn't be looking at it at all – just in time for the sound of something flashing to reach his ears.

Sherlock held still, refusing to move, barely even breathing as he curled up tighter into a ball.

"The city of New York would like to thank you for participating in our drill. Had this been an actual emergency, y'all would've been eaten 'cause you don't listen. You're ignorant." Sherlock wanted to complain, but knew better than to make a peep. "How a man come crashing through the back of a subway window… That's the problem with all y'all New Yorkers. Oh, we've seen it all. Oh no, a 600 foot worm, save us Mr. Black Man. And I come in acting nice, telling y'all to move to the next car, and you all just sit there like –" The man paused mid-rant, and for a frightening second Sherlock thought he'd been caught hiding, before he heard the flashing sound once more.

"Thank you for participating in our drill," the man said again, sound more professional this time, "Hopefully you enjoyed our new smaller, more energy efficient subway cars. Watch your step. You will have a nice evening." With the demanding suggestions the man was making, and the fact that he left a second later without any worry that the passengers wouldn't accept his poor excuse, Sherlock had a sinking feeling he knew exactly what that silver cylinder did with each flashing sound.

"Oh, Sherly, why are you curled up down there?" Mummy asked innocently as the people crammed into that single car slowly dispersed away.

Sherlock waited until they were out of the station and away from anyone wearing a suit, before he tested his theory. "Mummy, what happened on the train?"

Mummy cocked her head to the side, "Did you fall asleep, dear? It was just a normal train ride – there's nothing much to see underground."

"So it wasn't weird everyone was sitting in a half-eaten car?" Sherlock pressed on, staring intently at Mummy to gauge her reaction.

Mummy only laughed. "Half-eaten? I admit the car was a bit small, but it's just a new energy efficient project they were testing out. It's fun to help try something new, isn't it?"

"What about the giant worm?"

"Giant worm? Did you have a dream about a giant worm? That must have been scary," Mummy consoled without even a hint of recognition in her eyes.

Brainwashed. Fear tightened in Sherlock's chest, wondering if he would've become ignorant of the dangers that lurked in the underground as well if he hadn't acted so fast. "Sorry I couldn't save your memory too, Mummy," Sherlock murmured into her shirt.

"What are you talking about, Sherly dear?"

Sherlock shook his head, rubbing it into her blouse. The seven-year-old clutched at the hem of the shirt, refusing to let her go. "Mummy, we're never taking another ride on the tube without a weapon," he said seriously, even while she gave him an incredulous stare. "Next time," Sherlock began slowly as he tried to picture the perfect weapon against something so big and hideous. The other man threatened it with a tiny gun, but Sherlock didn't think he could pull off the same intimating look with something so small, "Next time, I refuse to board the tube without a harpoon."

… and it was a habit that stayed with him throughout his life.

A/n: Come on, tell me you all remember that harpoon scene in The Hounds of Baskerville!