Sam and Dean had spent the rest of the day leisurely walking about the streets of London. They visited shops and bought clothes here and there, wasting time in tourist areas when they grew bored of what they had initially been doing. Sam found more interest than Dean in visiting certain historical sites such as Churchill's bunker or the Benjamin Franklin house. Nonetheless, the murder they had crossed paths with at the beginning of the day remained at the back of their minds.

Sherlock's job was to solve murders – particularly those with which the Scotland Yard had difficulties. Seeing him at the given crime scene earlier didn't necessarily mean a supernatural creature had attacked. And yet, the brothers couldn't help but remember Castiel stating that the creatures of England were stirring and something big was coming. Furthermore, the angel had added that – though Sherlock's name wasn't mentioned as an important soul to the fate of the world – he was and would be important to the outcome of whatever was happening. In sum, so many facts kept the Winchesters restless and neither were even mildly surprise when a knock came at their door later that night.

They had initially been cautious. Word seemed to travel fast among the monster community and though they hadn't done much work abroad, Sam and Dean were definitely to be reckoned with and taken seriously by the mystical inhabitants. They readied their weapons, Dean gripping a silver blade whereas Sam wielded a loaded gun as the former carefully opened the door. Dean peaked through the small crack and paused for a moment, seemingly confused on who awaited on the other side.

"What is it?" Sam asked, clutching his gun a tad more tightly.

Dean looked back, his surprise and confusion blatantly evident as he opened the door wider, revealing John and Sherlock. John seemed a bit more humble than his partner, apparently wanting to have waited for permission to enter while Sherlock strode in as though it wasn't even mildly impolite. He followed in meekly, keeping his head down almost as though to camouflage his embarrassment and waited to be offered a seat before sitting while Sherlock had taken the liberty of making himself comfortable.

"Uhh…" Sam said slowly, alternating his gaze from his brother to the British guests, "Hi…?"

"Why are you here?" Dean said, freely displaying his weapon as he sat on the foot of his bed.

"Sorry for the intrusion," John began, looking over at Sherlock nervously – he was reading the brothers yet again, "But we need your help."

"With what?" Sam asked, though a part of him already knew the answer, "And how did you find us?"

"It wasn't particularly difficult." Sherlock brushed aside as though it was nothing, "Many signs pointed to neither of you being rich and having extravagant tastes. In addition, what with your claimed profession, it wasn't a far leap to deduce that you both traveled a lot and so preferred to deal with more questionable places so as to efficiently cover your trails if need be and buy the silence of clerks with greater ease. This specific location seemed to accommodate your needs flawlessly in every single way possible."

"Whoa." Dean said, dumbfounded.

"That's amazing." Sam cooed.

"Child's play, really." Sherlock assured as he pulled a folder out of his coat, "Now for the business at hand…" he threw the folder open on the coffee table, revealing images of the murder, reports made by officers on the scene and a detailed yet hasty analysis on the autopsies made. Sam moved closer, setting his gun aside, and gathered the documents, skimming through them, while Dean looked at the pictures. "This morning," Sherlock explained, "We received a call from Scotland Yard to assist in the murder of the Hathaway family. They believe some seriously troubled human cut-throat is the culprit however, due to the new information acquired about the world, we easily deduced that that was not the case."

"Why?" Dean asked, squinting at one of the pictures, "Seems like a horse trampled that one lady to death—"

"He's as daft as Lestrade—"

"Sherlock!" John snapped, kicking his friend and sending him a dirty look, "The Yard thought as much but no horse-drawn carriages patrol that specific area and no horse has been reported missing or escaped. Even so, it would have been spotted by many others before finally reaching the area of the murder and no calls have been made to indicate said possibility."

"Look at that," Sam said, pointing at an aspect of the photograph Dean held, "The plants are dead. Some powerful and evil entities are known to make things rot."

"That doesn't mean anything," Dean stated, "Maybe the Hathaways didn't know how to take care of them properly."

"But look at the ones indoors." Sam insisted, shuffling through them, "They're also dead. If they really failed at taking care of them, they would have thrown them out long ago."

"I guess," Dean shrugged but then revealed the photograph of the bloody kitchen, "But this looks like the work of your typical murderer – just, maybe a bit sloppier than usual."

"There's Madison written on the ceiling in blood," Sam stated, "I guess that can still fall in the hands of a human culprit but didn't the Bloody Mary ghost do something like that? She wrote the names of the victims her victims murdered in blood behind the mirror."

"Bloody—" John repeated in shock, "Did he just say Bloody Mary?"

"Yeah," Sam confirmed, "Long story."

"We ganked that bitch," Dean reminded, "It can't be her."

"But it can be something alike." Sam stated. "I mean, these little brands or taunts left behind aren't exactly exclusive to one species."

"We've done research of our own," Sherlock finally said, "I looked into Madison and found that she was Mister Hathaway's previous wife. She killed herself a year after her marriage to him and, soon after, he remarried. He used to beat her and though she sought help, it was never given to her."

"That's the perfect recipe for an angry spirit." Sam stated.

"Alright," Dean ceded, "Then that's what we're dealing with."

"Not quite." John said, "You see, Sherlock quickly noticed that there were two culprits to the whole matter. The trampled woman is the second wife of Mister Hathaway. We found bits of rotten flesh – horse flesh – around her corpse and about three pints of her blood was missing. The same also went with the family murdered in the kitchen."

"Doesn't sound like your typical ghost." Dean admitted.

"What do you think it is?" Sam asked, "Assuming you looked into that."

"The first is a nuckelavee." Sherlock said, "A rotten fusion of a horse and a man hailing from Scotland. They exist merely to make the lives of humans a living Hell and their breath is supposedly so dreadful it can wilt crops and sicken livestock."

"That would explain the woman," Sam nodded, "And the rotten plants."

"What about the missing blood and Madison?" Dean asked, admittedly surprised by the competence of Sherlock and John who had so recently learned the truth about monsters.

"At first," John explained, "We thought it was a vampire. However, those aren't typically found in England so we decided to look for a local variation or simply a similar one."

"Not to mention a vampire wouldn't have let all that blood go to waste." Sam nodded approvingly.

"We found that it could be a Dearg-due." John continued, "It's very similar to a vampire though it also has qualities of the undead. They can suck the life-energy out of a being and they have a taste for blood which would explain the missing pints. They're also known for holding nasty grudges against the family members that have wronged them."

"How are they born?" Dean asked.

"The information was a bit flimsy in those regards," John stated, "Generally, however, they seemed to be born out of rage, hate, misery and jealousy. We found many stories about them and Madison's mimics them to the letter."

"What do you mean?" Sam asked.

"Madison was originally from a poor family," Sherlock explained, "They were desperate for money and so they married her off to an abusive rich man, mister Hathaway. However, Madison was also in love with another man – one Mark Fitzgerald – but her farther forbade them from ever seeing each other again and so their romance ended as such. She eventually killed herself a year after her marriage to mister Hathaway, as previously explained, due to the police's lack of response in regards to her complaints against her violent husband. Her husband remarried almost a month after she passed away and her entire family was murdered exactly a year after her suicide."

"Wow," Dean said, taking the picture of Madison within the folder, "Poor girl."

"It looks like you've pretty much figured everything out." Sam commented, putting the documents back into the file, "I don't understand why you need our help."

"We need to kill them." John said.

"Figuring that out isn't particularly hard." Dean commented.

"Well, we know how to kill the Dearg-due," John said, "But we have no idea how to deal with the nuckelavee."

"Neither do we." Dean said, "This is literally the first time I hear about either of those things."

"Don't you have some sort of archive?" Sherlock asked, "I'm assuming that you supernatural-Hunters write down the things you notice and discover about these creatures for future references."

"Here's the problem with that," Sam explained, "There haven't been any Hunters in Europe ever since the colonization of America. They all left to pursue the monsters there and those who stayed behind eventually died out. We have virtually no information on monsters indigenous to the area unless if they're relatively famous."

"Then how are we supposed to deal with these things?" John asked, dismayed.

"Wait!" Dean exclaimed, "I know! The angel blade!"

"Angel blade?" John repeated.

"It's this super OP weapon that can kill anything." Dean explained, "So far, it's literally been able to kill everything except arch-demons and leviathans."

"Alright, where do we get one?" John asked.

"You can't exactly get one." Sam explained, "Only angels are allowed to have them and, after the fiasco we dealt with back home, Cas vetoed all of the ones Hunters and monsters managed to acquire. He's the only one out of all of us who has one."

"And he's missing." Dean remembered angrily. "Damn it! Where's that idiot when you need him?"

"Then what do you suppose we do of the nuckelavee and dearg-gue?" Sherlock asked, "You've been in this profession for quite some time, you must know some alternative."

"Well," Dean said pensively, "You know how to kill the dearg-due so we can deal with that but I literally have no idea on what to do with the nuckelavee."

"We'll have to do research," Sam said, "Find anthropology, history and folklore teachers and experts and scavenge libraries for more information. It could take a while."

"I hate it when we can't use the internet." Dean groaned.

"We, apparently, don't have much of a choice." Sherlock said, "I'll go to the library and find books on the matter, John," he paused briefly and looked at his friend, "Didn't you date a history professor?"

"Yes," John sighed, "Her name was—"

"Irrelevant." Sherlock quickly interrupted, "Go pay her a visit, charm her or whatever and ask for clarifications."

"We'll tag along." Sam declared, "You're new at this and, even if you're doing a good job, I'd feel better if you had professional supervision."

"Very well—"

"Awesome," Dean said quickly, "I'll go to Uni with Watson over there and you can go to the library with Sherlock, Sam."

Sam sighed at Dean's evident attempt at avoiding the most boring of tasks. Nonetheless, he ceded to his elder brother's desire and so they arranged a meeting time and place to get to work the next day. The final thing they exchanged to one another that day was a piece of advice the Winchesters were adamant in sharing: "Folklore and legends vary but that doesn't necessarily mean any of them know or tell of the actual way to deal with monsters."

I saw, for the SuperLock crossover, that people tend to pair Sam and John and Sherlock and Dean (as friends not as lovers) which is something I never understood XD

In my opinion Sam and Sherlock should be together and John with Dean. Sam is essentially like John in the sense where he's very human and intelligent (maybe even more than John) so Sherlock would probably be more comfortable with him than with Dean who is really immature (albeit smart) since, I think, Sherlock would lose patience with him. I also think that John and Dean have a compatible personality and have lived through similar experiences and so would be able to relate better.

But, in any case, my headcannon is still John getting along with both of the boys and Sherlock only liking Sam and picking on John XP