Disclaimer: nothing mine. Seriously.
A.N. If you didn't read the Devil's Foot, want to and don't like spoilers, turn tail now. Seriously. Last chance. :-)
For once, Sherlock is the one left to settle the taxi fare, while John storms off. When he catches up, John still won't talk to him. He won't even look at Sherlock, and marches up the stairs to the flat and, then, his room. The detective is all for giving his only friend time to cool off, but there's ominous rummaging noise coming from the room, and not the 'where did I hide the good scotch' kind. So naturally Sherlock lets himself in to check.
What he finds steals his breath away. John is not unpacking after the trip. He's packing – his favorite jumper, the box where he 'hides' things of sentimental value. He's leaving. Permanently. Breathy, his throat still sore from all the screaming earlier in the day, the detective utters, "You can't." Even if John can, of course. Sherlock expected it from day one, in truth. He thought it'd happen much sooner.
"I'm sorry?"John replies, cold and controlled, stopping abruptly like he hadn't done at the sleuth's intrusion.
"You can't," Sherlock reiterates. Not now at least. Not until he hasn't managed to delete his overstrained brain's previous production.
"I think you'll find out I can, Sherlock. I'll let Mike know you're back in the market for a flatmate," the doctor states, going back to his task. Still not screaming, not accusing, just very matter-of-factly, and it terrifies Sherlock more than anything he'd ever seen.
"John." It's not an entreaty, not exactly, but it still sounds a lot like one.
The doctor stops again. "No, I...I can't stay. Not after what you did. There's madness I happily follow, there's madness I get pulled along with, and there's madness I can't abide. This is where I stop," he tries to explain. He won't ask Sherlock to be not-Sherlock, it wouldn't work and it wouldn't be right, but he can't let himself be overwhelmed by his crazy flatmate again. He just can't.
"It was an accident," Sherlock counters.
"No it wasn't. A fire hazard is an accident. With you, a Vibrio Cholerae contaminated fridge might be an accident – and no, that wasn't a suggestion. What you did was attempted murder-suicide." There. It's out in the open.
"No, John!" the detective objects, as loudly as he can manage.
"I must have misunderstood then. I'll tell you what happened by my point of view, but feel free to correct me," John offers.
Sherlock nods briskly.
"You agreed to come on a holiday with me because you had run us ragged with nonstop cases lately," the doctor starts. Something Sherlock can't dispute. John had said it was either this or being admitted when they'd undoubtedly soon collapse, and the detective had caved in.
"Still, someone managed to get killed in the most somnolent village of all Cornwall, mysteriously too, and you just had to look into it. I didn't complain." Their vacation was near the end anyway, they had recuperated a bit and John was almost bored to tears. Of course he didn't object.
"You discovered that the victim had been poisoned, and deduced that a local scientist had a grudge against him. The man had spent a lot of time abroad and could reasonably have come across some rare poison whose traces our forensics couldn't even imagine how to individuate. Not that you walked me through it." John had gleaned as much after the fiasco, when Sherlock had insisted on going to the police to offer them the answer, but the constables looked doubtful of the still wild-eyed detective. John isn't sure they'll take the man in. Sherlock would have gotten the murderer to confess, if standing hadn't felt like an herculean effort at the time. When John said he'd go back to London, with or without him, the detective had relented. Not his fault if they couldn't close a case already solved for them.
"So you committed a little breaking and entering, forgetting to let me in – again – and took a sample of the poison. A poison that you had determined had been burned in the victim's room. Then we went back to our room, and without telling me anything, you proceeded to set your sample afire. Yup. Attempted murder-suicide," John concludes.
Being merciful to them both, he doesn't insist on the poison's effects. There's a reason the victim didn't run from the poisoned room or called 911, and it wasn't instant acting of the toxin. The poison doubles as a drug, causing the most gruesome hallucinations. John is just relieved they hadn't morphed into a flashback episode, because otherwise they'd be dead. Instead Sherlock screaming his name with abject terror and despair, still deep in the throes of his own nightmare, had kick started John's adrenaline and freed him from the paralyzing hold of his delusion. He had managed to drag Sherlock out before falling in a panting heap beside him.
"I didn't mean to kill anyone, John. But there were a lot of substances which might have been used as the murder weapon in that man's home. I chose the most probable, but Baskerville taught me that I needed to make sure of such things. Especially if I wanted to persuade those idiotic policemen. You saw I still didn't. There I lacked my lab equipment, and I couldn't commandeer the use of their labs either. I took a sample many times lesser than what the killer had used on the victim, calculating it from the quantity of ashes produced, so I thought we'd be safe. A bit worse for wear, but safe," Sherlock explains. John's glare shows that mentioning Baskerville has been a decidedly wrong tactical move.
"And you haven't considered, given the size of his grudge, that the man could opt for overkill?" the doctor counters, flabbergasted. Sherlock must have encountered overkill on some of his cases. Hell, he practically inspires it – when a Yarder will finally snap and get rid of him, s/he will definitely want to be beyond sure the pesky consultant is really gone.
"I excluded it because the poison was hard to come across and I thought a scientist would want to have as much as he could for further experiments. But taking into account what that man did to the murderer's lover...John, why didn't you say this before? I need my conductor of light!" the sleuth argues, going wide eyed with realization half-way through.
Oh. Splendid. He gets it now, John internally huffs. He tried to be calm and aloof, since he was leaving Sherlock, and nothing regarding the detective concerned him anymore, but that last sentence shoots all his resolutions.
"Are you trying to say it's my fault because I didn't say this before?" he – finally – yells. "How could you not think of it after what you've done to that CIA agent who threatened Mrs. Hudson, hm? Even someone as emotionally challenged as you should understand that there's no holding back or thinking about bloody experiments in revenge!"
John has morals. He's a good man. He tries his best to be, at least. When he heard Sherlock reveal exactly what the murder's reason was, though, he marveled at the means chosen. He knows first-hand (thanks to Sherlock) exactly how awful that poison is. Still, the victim wasn't a nice man. Not at all. If he'd done to John's girlfriend (or Harry; or Sherlock, even) what he did to the girl their murderer loved, John wouldn't have been content with poisoning. Nothing as easy as an eye for eye for him. That's what it was; the bastard had done what Sherlock did earlier – and poisoned a girl with it. Over money. John would have wanted the man's blood on his hands. Plentiful. He would... he's not entirely sure, but it would have been an interesting crime scene. Probably lots of body parts to play with. And Sherlock didn't think such a motive implied being prodigal with the poison of choice?
"He realized it after years," the detective protested, clearly disgusted at the idea of such a slow dawning of the truth in the mind of someone who calls himself a man of science. He would have understood what had happened in minutes at the most, if the murder weapon was known to him so well. "I discounted love as a factor – he should have moved on from her long ago. I only considered the rage at being used as dealer of an untraceable poison – well, untraceable for these morons – when causing death was the last thing he wanted."
John's eyes roll almost without conscious intent. Sherlock is...Sherlock. Still the man who wondered why a woman would think about her dead daughter years later.
"So I was wrong. Wrong, careless and blind," the sleuth admits, so quickly he's almost tripping over his words, but still talking distinctly enough there's no misunderstanding him.
The doctor represses the urge to check if Sherlock is running a fever as a consequence of the poisoning. Talking about Baskerville, John remembers well the verbal gymnastics his friend did in order not to confess he'd deduced wrong. This is unexpected.
"But I never meant to kill you, John. I can't honestly say I meant absolutely no harm, but honestly the furthest thing from my mind was your murder. Or my suicide. Even if I went psycho, I'd never aim for both. Murder-suicide is what lovers do. Or stalkers," the detective earnestly attests.
"That's why I found it believable. Your behaviour whenever I manage to get a date is definitely stalkerish," John quips with a smirk.
Sherlock doesn't protests. He doesn't defend his attitude. He just grins back.
"You did it on purpose!" the doctor shouts then.
"What?"
"I can't flee from someone I'm joking with, can I?" John replies. He was so sure he needed to get away a minute ago. But Sherlock had not tried to kill them (that had haunted him more than the poison-induced nightmare). The detective had just been his usual selectively idiotic self. Yes, John could have died. Sherlock definitely will without someone to take care of him. So how can John go?
"You jested all on your own, John. But if it helps, I won't slip you anything that needs testing in the future," Sherlock promises. Each time he tried it, John's reaction was strongly adverse after all. Sherlock can learn from his errors. When it's worth it.
The doctor doesn't reply, but his one of his eyebrows shoots up in deep disbelief.
"At least without getting your consent previously," Sherlock emends.
"That would be nice, thanks. Tea?"