A/U: My first Sherlock fic! The verse at the end is from "Romance" by Edgar Allan Poe.

String Theory

John sits in the flat in the dark, his gun gripped in his hand, and he listens.

Sherlock has been gone for one hour and 17 minutes.

As he waits, John thinks of the bodies, four of them in two weeks. All were seemingly targeted at random and were found arranged in the traditional funeral position, their hands crossed over their chests and their bodies and clothes neatly straightened, with red rings of sliced flesh encircling their necks. There is very little physical evidence for the police to identify the killer by, only some footprints indicating that he has a very common shoe size, and a single strand of hair that currently resides in a plastic bag on the table next to where John is sitting.

Genius needs an audience, and this killer has found one in John Watson.

This is the truth as John knows it: Sherlock Holmes will never catch the killer, because Sherlock Holmes is the killer. This is the list of evidence that John has compiled: the filament of black curly hair, the killer's precise nature, the matching shoe size, Sherlock's rather sudden habit of late night walks…and, of course, the treacherous violin.

Only Sherlock, John thinks wryly, would murder using violin strings.

He wasn't very surprised to discover the truth. Not really. Hadn't Donovan, when he first met her, warned him that one day Sherlock would be the psychopath leaving bodies in the streets? So it's not surprising but it is distressing, because what happens when Sherlock completely loses control, when he starts killing not strangers but people he knows? What separates Anderson, Donovan, Lestrade, Sarah, or John himself from those who have already been targeted?

John can't help but think that Sherlock won't hurt him, at least for a while... but Sherlock will get bored with his little pet eventually (and Moriarty may have been a bastard, but he was a perceptive bastard who saw John as he really was, and for that John is strangely grateful); it is only a question of when, not if.

John wonders if he could shoot Sherlock, if the other man attacked him. He thinks he could, assuming that Sherlock broke his routine and attacked John from the front, instead of sweeping quietly up from behind, the twisted rope of steel core strings wrapping swiftly around his neck and cutting off his air, breaking through the skin as effectively as a knife, leaving John unable to scream… John shudders and puts that image out of his mind.

Sherlock has been gone for one hour and 23 minutes. When he returns, John will be sitting here. He will get the answers he needs tonight.

He shifts the gun in his hand, and he waits.

That little time with lyre and rhyme

To while away- forbidden things!

My heart would feel to be a crime

Unless it trembled with the strings.