Disclaimer: I don't own

Author's Note: After a request on livejournal I'm writing my first crossover between my two favourite shows. Enjoy!

"Why are we here again, Boss?" Tony asked as he craned his neck searching for his bag through the crowd. He was standing beside Gibbs, whose bag had already been found while Tim and Ziva had gone looking for a trolley and their ride to the hotel respectively once their bag had come. Even Ducky had his, and was now happily chatting to anyone around him who would listen. His accent always had them believing he had just come home and he seemed to love using that as an opening to tell them his life story.

"We're here because a marine is dead." Gibbs said shortly.

"Yeah, but why us?" at Gibbs' glare he quickly added, "Not that I didn't want to come, but can't the local police have handled it?"

Gibbs huffed as he returned his attention to searching for Tony's bag. "Father has enough influence in high places to get us here, and not enough trust in non-Americans to want us here." He said bitterly. Gibbs had made no secret of the fact that the director had ordered him to come and to co-operate with the local authorities.

"Ah-ha!" Tony suddenly stated, dashing for the bag he had just spotted. He quickly confirmed it was his. Tim was standing by Gibbs when he returned, helping the Boss load everyone's bags on it.

"I have found our ride." Ziva stated as she made her way over to the group. Ducky finished up his conversation in time to hear the woman by Ziva's side introduce herself.

"I'm Sergeant Donovan from Scotland Yard, and I've been asked to escort you all to our crime scene."

"Wouldn't it be better if we went to our hotel first?" Tim asked, 'So we can freshen up a bit.'

"Yeah, it's not as if the crime scene is going anywhere." Tony added.

Donovan shook her head. "There's been a second murder."

That was all it took. Instantly the entire team drove thoughts of hotel rooms out of their heads. Donovan turned to leave, but Gibbs stopped her. "McGee, David; find a taxi and go to Scotland Yard. Start going over the first murder. Ducky, DiNozzo you're with me."

"Ah Boss, do you want Ziva and me to drop our bags off at the hotel first?" Tim asked. Gibbs gave him a cold stare and then left with Donovan.

He did, however, leave the bags with Tim.

As they arrived on the scene, which was a small house on a deserted back street of the outskirts of London, all three Americans were shocked to see a member of the public standing by the door. Donovan, however, seemed disgusted to see him there and barely parked the car before she was moving to his side.

"Freak inside then?"

The short, blonde man who was wearing a brown, woollen jumper and looked remarkably unremarkable gave Donovan a hard stare. "Don't worry, Sergeant. He's gone."

Donovan looked thrown. "Why are you still here then?"

The man nodded towards Gibbs and his team. "Them. He wanted me to meet and give my opinion of the American police."

"He trusts your opinion?"

The man smirked. "I find, if you don't insult him and actually use your intelligence, he will trust your opinion to a point."

He then moved pass her to stand in front of Gibbs. Gibbs glared at the man as he gave him a quick searching glance.

"Which one, Navy or Marines?"

"Excuse me?" Gibbs asked.

"You have a military stance and you work for a military agency focused on the Navy and the Marines. Therefore you must have served in one of those, or you would be in another agency. So, which one?"

Gibbs narrowed his eyes. "Marines. Who are you?"

"John Watson." John said, holding out his hand. "And you are?"

"Special Agent Gibbs." Gibbs said as he ignored the hand. "This is Special Agent DiNozzo and Dr Mallard. Why are you on this crime scene? "

"A few reasons. I'll introduce you to the main one soon." John said as he lowered his hand and headed for the crime scene tape.

"Wait, how did you do that?" Tony asked. "That was awesome, man!"

John turned to Tony, "That was nothing." He said with a smile. "Just a trick I've picked up and can never do as well as the man who taught me."

With that cryptic remark, he walked away.

"Who was that?" Ducky asked Donovan as she led them to the body.

"The sidekick of a major pain in the arse of Scotland Yard. The less said about that pair the better."

"Pair?" Tony asked, but Donovan refused to answer and instead introduced them to her Boss who was standing by the body.

"Detective Inspector Lestrade. Inspector, this is Agent Gibbs and DiNozzo and the NCIS medical examiner Dr Mallard."

"You brought your pathologist?"

"Technically, my dear fellow, I decided to visit my homeland and stopped to help Gibbs out on the way over."

Lestrade's eyebrows rose. "You're Scottish?"

Ducky bent down to examine the body. "I believe my accent would prove that point without any further evidence. Now my boy, what happened to you?"

Donovan glanced around the room and turned to Tony. "Who is he talking to?"

Tony pulled on a pair of gloves as he answered. "The body."

"Why?"

"Because Sergeant, while my patients may be dead, it doesn't mean I can't treat them with respect." Ducky cut in. "Anthony, would you so kind as to hand me the liver probe from my bag?"

"Here you go, Ducky."

"DiNozzo, I want you to bag and tag everything."

Donovan turned to Lestrade. "Are you just going to let them take over our crime scene?" she demanded.

"If it means they take over dealing with Sherlock, yes." At her disbelieving look he continued, "Sergeant, they're here to solve this case and personally, I would rather give it to them and work on other cases, knowing they're only working this case and can give their full attention." He broke into a sly grin. "Plus, it may shake Sherlock up a bit."

Donovan smiled in return and turned to see if she or Anderson could help.

"McGee, what have we got so far?" Gibbs demanded as he strolled into the conference room the NCIS agents had been allocated while in London.

"So far Boss, we have three deaths and a lot of assumptions." McGee stated as he dropped the file he was holding onto the table and grabbed a photo from it.

"McGee-"

"Sorry Boss, but some of the notes in that file don't make sense as there is no evidence to support them." He placed the photo onto the whiteboard in the room.

"This is our first victim, John Walkers. He was found in a locked room, two blocks away from his actual home. He was found hanging from the ceiling, though he was actually killed by some unidentified poison. They still haven't gotten the results of the tests for that yet. He didn't have a girlfriend or any siblings, both his parents are dead and all his close friends have some form of alibi or no motive to kill him. The strange thing is-"

"What is strange, McGee?" Tony asked after a long pause.

"There's no evidence of this being investigated as a suicide. It looks like a suicide, except for the fact there's no note and the door was locked from the outside but this was always assumed to be the first identified kill of a serial killer."

"We'll have to ask our friendly inspector about that, McGee." Tony said. McGee shrugged and stuck the second photo next to the first.

"Yeah. Anyway, our second victim was Staff Sergeant Jonathon Winston who was on vacation here during his two weeks of leave. He just returned from a two-year duty in Iraq and while he wasn't well liked in his unit, they all have the alibi of not being in the country when he died. In fact, he had barely been here two days-"

"Doesn't mean he couldn't have made an enemy, McGee." Gibbs interrupted.

"I know, Boss. He was killed the same way as the first victim according the Met and they're also running tests on him to find the fatal poison. What did you guys find on the third victim?"

"Not much yet, McGee. He had ID on him, identifying him as a-"

"What is it, Tony?" Ziva asked.

"Johnny Wiggles. Is it just me, or there a connection between our three victims?"

"They all have first names of 'John' and a last name beginning with 'W'" Gibbs stated. "DiNozzo! What was the name of that man on the crime scene?"

"What man?" McGee asked.

Tony ignored him. "John Watson, Boss. Think it's related to this?"

"It's one hell of a coincidence. DiNozzo, you're with me." Gibbs stormed out, looking for D.I Lestrade.

Lestrade had quite willingly given them John Watson's address, on the condition he came with them. When asked why, he just mentioned something about a show and eyes in microwaves and clammed up.

At 221 Baker St, Tony knocked on the door to be greeted by an elderly woman who introduced herself as Martha Hudson and recognised NCIS without them explaining who they were. She explained that she had lived in Florida for years and her husband had had a few run ins with NCIS as she led them up the stairs to 221b.

"John," she called as she knocked on the door. "There are some agents from an American agency to see you." She turned to her followers, "Such nice men they are, John and Sherlock, even if Sherlock is a bit odd. They always help me out when I need it and John is such lovely company when he's between jobs."

"Which is far more often than I would like, thanks to him." The man from the crime scene, John Watson said as he opened his flat's door. He had clearly caught the last moments of conversation.

"John Watson, we have a couple of questions to ask you." Tony said as he moved past Mrs Hudson. "Mind if we come in?"

"Sure, but I'm afraid you'll have to stand. Our chairs are…out of commission." He moved back to let them in and Mrs Hudson caught sight of the burned lounge chairs and sofa.

"Sherlock, what did you do to my bloody chairs?"

A tall, slender and black haired man poked his head out from the kitchen. "Nothing, Mrs Hudson. These are John's from storage. I swapped them for yours for the experiment."

"I never did thank you for that, did I?" John grumbled as he walked over to the kettle. Mrs Hudson huffed and left the flat, closing the door behind Lestrade who was grinning.

"You weren't using them and I needed to-"

"Sherlock, I don't want to know so long as you get rid of them. Tea, anyone?"

It took a moment for the NCIS agents to realise he was talking to them. They had been using John's lack of attention on as an opportunity to examine the flat. It was a complete mess, which fitted the fact that two bachelors lived here. There was also a skull sitting on the mantelpiece, next to a knife, which was holding what looked to letters there. There was a violin leaning against the overfull bookcase and a Union Jack pillow lying beside it.

"Umm, no thanks. Look, John we have few questions to ask about t-" Tony said.

"Oh how boring." The other man, "Sherlock", suddenly interrupted. He ran an eye over the two agents, much like John had earlier but he gave the impression of having seen your soul and found it lacking.

"What is, Sherlock?" John asked.

"They think you are the killer as you share the same first name and last initial with the victims."

"And you don't think that's a realisable conclusion?" Tony asked.

"It's a conclusion worthy of the idiots at Scotland Yard who don't observe anything even if it's right before their eyes! John clearly isn't the killer, as the killer was at least six foot tall and John-"

"Is not." John interrupted, gaining a glare from Sherlock, which he answered with a shrug.

"And how would you know that?" Gibbs said stepping forward into Sherlock's personal space. Sherlock didn't seem intimated and had a smug grin on his face. "Because, our killer was tall enough to hang the first victim from the roof using only a small stool he found and replaced in the bathroom. He was also able to overpower a man who had just returned from active service in Iraq, which I don't doubt John could do but not without injuries to himself which he doesn't have. Besides, this man has been killing for years and John only returned to England a year ago and was not capable of these crimes for at least two months."

"You can't possibly know that. How could you know this is a serial killer?" Tony asked, dumbfounded.

"The same way I know your Boss has been married at least twice, with at least one wife dying, and was a Marine. He builds a large wooden item, likely furniture in an enclosed room on a regular basis. He dislikes fools and is in the habit of striking you on the back of the head when you say something foolish. He also prefers coffee. You both came here with at least two other people, one of them a woman and another who is British. You, Agent DiNozzo, have never been married and live in a flat of similar status to ours. You have suffered from some severe illness related to your lungs and have an extreme amount of trust in your boss. You have a fascination with films, especially the James Bond ones John loves and would like to see yourself as being thought as 'cool' as them."

The two agent's jaws dropped. Sherlock smug smile grew.

"Figuring out our killer was a serial killer was simple compared to that. Coming, John?"

He grabbed his coat and scarf, throwing John his as the two agents tried to get over their shock. The two men were out the door and down the stairs before they managed it.

"Lock it on your way out, will you Inspector?" John called as the door slammed shut.

"What was that?"

Lestrade's grin grew. "That was Sherlock Holmes."