I neither own nor profit from any of these characters; they are the property of Sir Arthur Conan Doyle, Steven Moffat, Mark Gatiss and the BBC.

If you see something that you think ought to be changed or improved, please feel free to let me know, if you'd like. Constructive criticism is always welcome.

Written for a one-word prompt ("nicotine") from Feej; special thanks to her for having read this over for me.

Radio Hamlet has done absolutely gorgeous fanart of this story here (is . gd / exhale). Please go and take a look - it's quite amazing.

Lestrade inhaled deeply, held the smoke in his mouth for as long as he could, then let it out in a thin stream, watching it curl into the cold air around him. He liked to take his time with a cigarette, let it spread slowly over him and take the blade-bright edges off the world so that he could focus on the rigours of his work. The Detective Inspector was a busy man and had little time to relax; these breaks were short, but they were all he had and they helped him keep his footing in the constant onslaught of work at New Scotland Yard.

The nicotine rush was the only thing that helped him get through the day sometimes. He needed that.

"Haven't you finished yet?"
Lestrade looked up. Sherlock was staring impatiently at him, pacing back and forth – either to allow his overactive brain some outlet for its energy, or simply to fend off the cold.
"No, I haven't, Sherlock. This is my only time off, and I'm going to take as long as I please."
"How can you possibly still be smoking that same cigarette?"
"Not all of us smoke so fast we practically swallow them," Lestrade replied. Sherlock didn't look bothered by the comment, but started pacing faster, and in circles around Lestrade, until the inspector gave up on trying to finish his cigarette and simply got rid of it.
"Never," Sherlock replied. "Come on! There are serial killers waiting!"
"Hardly waiting," Lestrade sighed, though he followed the younger man back into the building. "These cases are all ten years old at least."

It was Lestrade's rule, and one that grated on every fibre of Sherlock's being, that Sherlock was not allowed to touch any newer case files. For one thing, he hadn't known the young man for very long – though to hear the way he bandied his self-chosen title about, "consulting detective," you'd think he'd been working with the police for years – and for another, Lestrade actually had quite a bit more authority than his position indicated, and he had the reputation of the entire department to consider. God forbid the public should find out they were letting some young cut-up dig around in any of their files, much less fresh ones.

Sherlock hadn't given in quietly, of course. Nothing about that man was quiet. In fact, Lestrade still caught him every so often, devising ever more creative ways of getting his hands on what he called "the really interesting ones." But the archive secretary had been warned about Sherlock, and Lestrade brought her coffee on mornings after she'd had to deal with a particularly put-out "consulting detective," so between them, they managed to keep Sherlock at bay fairly effectively.

He tried again that evening in Lestrade's flat. He had a place of his own, yet somehow, every time Lestrade walked out to his kitchen for a coffee, or into the living room for a quiet bit of sports (he watched the football quietly, because his team was awful and there was never any reason to cheer), he tripped over sprawling limbs and scattered papers, and discovered that Sherlock had staked out a temporary residence for himself on Lestrade's floor. Again.

This time, he was making a play for a new case that had come in that afternoon, trying to convince Lestrade that it was somehow related to another one he'd given Sherlock weeks ago.
"Really, I would've thought you'd want it solved," Sherlock told him, his hunger for the case warring with his natural disdain and no clear winner showing itself.
"I do want it solved," Lestrade agreed. "That's why I've put the team to work on it."
"No, I meant solved," Sherlock growled, shaking his head. "Not horrifically bungled by Anderson and anything useful destroyed afterward."
"Anderson's on the team for a reason."
"You need someone convincingly slimy for undercover operations?"
"Maybe I just keep him on the job so you won't want to go anywhere near it."
Sherlock paused. "If that's actually your plan, you're cleverer than I thought."
"You can't have the case, Sherlock. Go solve something else."

He needed another cigarette after that. He was starting to smoke more at home than he did at work. This time, at least, Sherlock didn't follow him.

Then again, it might have been better if he had. Lestrade walked back into the flat to discover that Sherlock had, in fact, taken a smoke break – only he'd taken it on Lestrade's couch, spread out over a thick coating of case files. There was ash in Lestrade's half-finished drink.

"Sherlock, what the hell is this?"
The younger man raised an eyebrow at him from where he was entangled with paperwork and cushions. "The Robinson murders?"
"Don't you 'Robinson murders' me, you know exactly what I'm talking about. You can't smoke in the flat!"
"Actually, I've just tested that hypothesis, and it turns out I can."
"No, you can't! You don't rent here, I do, and I'm the one who'll get booted!"
A shrug. "You can come stay at mine if you like."
No, he bloody well didn't like. Where Sherlock lived, Lestrade might as well note his own name down in his case files now and save some trouble for whoever would eventually be investigating his murder. Peckham wasn't exactly lovely at the best of times, and the staircase to Sherlock's flat was a minefield of old syringes and the people who had used them too liberally the night before.
He snatched the cigarette from Sherlock's fingers and put it out against a paperweight, dropping the remainder of it into his Bruichladdich, which was by now completely undrinkable. (Not that it had been particularly drinkable before, he thought wryly. Only the best in single malt for him. Ha.)

In the morning, he announced, "We're quitting."
"Quitting what?" Sherlock wanted to know from his prone position on the couch. "I can't quit. I'm freelance."
"Quitting smoking," Lestrade told him, and dropped a box of nicotine patches unceremoniously on the younger man's chest. "Starting now."
Sherlock tipped his body sideways, so that the box fell off onto the carpet. "I don't recall agreeing to quit. For that matter, I don't recall wanting to quit."
"Well, you are."
"No, I'm not."
"You are if you want any more cases from me. You're a hazard to the evidence. You're putting my flat at risk. And most of all, it's going to drive me mad if I have to watch you smoke while I can't. So either you're quitting, or you're giving me back the case files and finding something else to do."

Lestrade hoped to God Sherlock didn't decide to give back the case files. He was quite certain he would suffocate from the paperwork alone, which would make quitting smoking rather pointless.
He waited.
Eventually, a hand snaked down from the heap of Sherlock on the couch and snagged the nicotine patches. "These had better be bloody good."

Apparently, they were. Or at least, they were the way Sherlock used them. Lestrade had never had a headache the likes of the one that assailed him over the next few days. Every time he walked past a shop, his eyes caught and held the stacks of boxes behind the counter and he thought, they would make it all go away. Every time he entered Scotland Yard, he closed his eyes and gritted his teeth and didn't inhale again until he was well inside the doors, away from the assortment of office workers standing about in the cold, smoking – well, they were cigarettes, but they might as well have been nectar and ambrosia.
Sherlock didn't seem to have those problems. In fact, it didn't seem to affect him at all. When Lestrade confronted him about it – how the hell was he so chipper? – he simply shook his head. "Mind over matter," was all he said on the subject.

Lestrade caught him one day, putting on a patch.
"You've already got one on."
"I'm not an idiot, Sherlock, I can see it."
"I haven't got one on. I've got three on."
"You're wearing three patches?"
"Of course. Brilliant for brainwork."
"Sherlock, that can kill you!"
"Can it?"
And Lestrade had to admit he didn't know, really.
In the end, they compromised, insofar as Sherlock ever compromised. Lestrade agreed to let Sherlock have his three patches, and Sherlock agreed not to gloat.
At least one of them kept his end of the bargain.

It was almost worse having Sherlock on the patches, Lestrade thought. Before, when the detective was filled with the hyperactive agitation of a half-solved case, he would at least go and do his frantic pacing outside, cigarette in hand, as if the answer were somehow to be found in glowing ember and growing ash. Now, though, he had no reason to leave the flat or Lestrade's office, and so, no matter where he was, Lestrade was constantly subjected to the steady rhythm of Sherlock's shoes against the floor, the noises of impatience that escaped him, the never-ending drumming of his fingers against every available surface until
he exploded.

There was a momentary break in the detective's pacing. "What?"
"You haven't stopped moving all day! I've got the worst bloody headache of my life, and you're it!"
"What would you like me to do?"
"Anything, as long as you do it quietly!"
"Anything?" asked Sherlock and, too late, Lestrade caught the gleam in the younger man's eye as he glanced toward the papers spread out over Lestrade's desk.

He shouldn't. He knew he shouldn't. But his eyes were bloodshot and his head pounded and his fingers twitched and he missed his nicotine rush and my God, he would do anything to make it easier, so he snatched the stack of files up wholesale from the desk and thrust them into Sherlock's arms.
Sherlock went.

The call came in at about four o'clock, a body in a warehouse, discovered by a couple of day labourers (ironically, on their smoke break). When Lestrade went out to report to the scene, he found Sherlock waiting by the response car.
"You can't come!"
"You gave me the files."
"You're welcome."
"How can you expect me to solve the case with incomplete information?"
"I don't. I expect you to bugger off and leave me in peace for a few hours."
"Which I've done," Sherlock pointed out, "and now I'm helping you close the case." He climbed into the back seat of the car and, without another word, shut the door on Lestrade's indrawn breath.

"One word," said Lestrade as they drove to the scene, "and I swear to God I'll turn this car around."
"Quitting has done wonders for your attitude," Sherlock muttered, but at least he had the sense to do it under his breath.

When they arrived at the warehouse, Sherlock shot out of the car and was waiting impatiently at the barriers by the time Lestrade caught up. Sally Donovan was posted at the perimeter and was giving Sherlock her best glare; Sherlock was doing quite a satisfactory job of glaring right back.
"Ladies," Lestrade said.
"Sir, what's he doing here?" Donovan wanted to know.
"I…" God, what was he doing? He pinched the bridge of his nose, trying to rub away the headache and the stress. "He's helping with the case."
"Is that allowed?"
No, of course it wasn't. "Are you questioning me?"
"No, sir. Sorry, sir." But she didn't stop glaring as the young detective followed Lestrade under the tape barrier and into the warehouse.

Once they were inside, though, Sherlock's face lost all its bitterness. He grinned as he looked around the scene of the murder; his smile widened every time his eyes paused, fastened on some subtle signal Lestrade couldn't even begin to fathom. The inspector very nearly smiled in return – seeing Sherlock actually happy was a rare event indeed – but then his head gave a particularly painful throb, and he decided that, as Sherlock wasn't even supposed to be here, the least he could do was to suffer alongside Lestrade.

"It's a crime scene, Sherlock, not a bloody funfair."
"Says the man who visits them for a living."
"Shut up. You wanted to come here. So do your thing."
"Oh, I am."
Lestrade shifted his weight from one foot to the other, waiting for Sherlock to finish doing whatever he was doing.
"Stop that."
"Stop what? I wasn't doing anything."
"Moving. Breathing. Waiting."
"I can't stop breathing!"

Another few moments, and Sherlock's eyes flickered away from the body in front of them. "Finished."
"What did you do?"
"I observed."
Lestrade sighed. "Bloody hell. Anderson!"

As the forensics team moved in around them, Lestrade pointed them here and there to start sweeping for evidence, then drummed his fingers nervously against the side of his leg. He was getting as bad as Sherlock – the twitching, the mood swings.
Patch, he thought. Maybe it was running out. No, these things were supposed to last all day, weren't they?
What if he put on another one, like Sherlock?
No. One of them dancing on a self-destruct button was enough.
He drummed his fingers.

Astonishingly, Sherlock left him alone after they got back to the station. In fact, Lestrade didn't see him again all evening. He kept checking over his shoulder as he moved about his flat, making tea, looking up the football scores (another loss, hardly unexpected), as if he expected the "consulting detective" to show up out of nowhere and snipe at him for having disturbed the landslide of papers on his couch. Though how he could ever tell, Lestrade had no idea.
He thought about going to bed, but he didn't feel like sleeping – ridiculous; he hadn't had a proper kip in ages, was he turning into Sherlock? – so he pushed a few more papers aside and sat on the edge of his couch-turned-filing cabinet, turning on the television so that he could stare at news reports and only-halfway-funny sitcoms without really paying attention.
He drummed his fingers.

When Sherlock picked the lock, sometime close to midnight, Lestrade had buried his face in his hands, fingers pushed roughly through his hair, still wide awake. He heard the detective come up the stairs (never quiet, even in the middle of the night), but didn't bother to react.

"What have you done to my papers?"
"What have you done to my couch?" came the groaned response.
"You want answers. I need space to work."
"Well, I needed space to watch television."
"You're not watching."
"Very observant."

There was a shift beside him, and suddenly a messy heap of limbs and suit and hair was on the couch, crushing the case files Lestrade ought not to have in his flat at all.

"Today, the killer. It was the brother."
"How do you – " Lestrade shook his head. This shouldn't surprise him, even though they'd only learnt late that night that the victim had had a brother at all. When was there ever anything Sherlock didn't know?
"Obvious. First, there were the cuffs on his shirt. Frayed at the edges, but – "
"Bloody hell, Sherlock."
The younger man paused in surprise.
"How do you do it?"
"Simple. I observe."
"Not that. I don't care about the case, it's the middle of the night and I'm not paid to care again until morning. This." And he pulled up his sleeve to indicate his meaning.
They both stared at the nicotine patch, and then Sherlock pulled up his own sleeve. Three.
"Mind over matter."
"It looks more like mind over death by nicotine overdose from here."
"Don't be silly; I've calculated the amount exactly."
Lestrade buried his face deeper in his hands.

The papers shifted again, several more fluttering to the carpet, as Sherlock drew his legs up under him and wrapped his arms around them.
"When I say 'mind over matter,' I'm not being trite," he said. "It really is. My body may crave the nicotine, but my mind craves the rush. It's the rush I wanted, the way it makes my brain feel, lets me think. Everything else is just transport."
"And three patches does that for you. You don't miss the feel of it in your fingers, against your lips. You don't miss the taste…"
"No," Sherlock said.
"Well, I do."
"I mean no, three patches doesn't do that for me. You've done it for me. You gave me a new rush – the cases. You gave my brain something real to do. The patches only help me do it."
Lestrade was silent.
"Besides, I've been through worse."

Memories of Sherlock in withdrawal, clawing at his own skin, sweating through the sheets on his bed, shaking in Lestrade's arms.
Yes, he had been through worse.

He couldn't think what else to say, so he made a poor attempt at an apology, not quite sure why he was making it at all. "Sorry. I should have thought…"
"No, you shouldn't. Why would you? Anyway, I'm fine. With the cigarettes and the other stuff."
"And the cases help with that."

They were quiet for a long time.

"I've got a follow-up on the Weeks case tomorrow," Lestrade offered. "You could come along."
"Sergeant Donovan might object."
"Keep your mouth shut and she won't be able to," the inspector sighed, though it was true. Sally would object, and she would be right. It didn't mean he wasn't going to let Sherlock come anyway, just as he had that afternoon.
In for a penny, in for a pound, he supposed.

"I don't understand," Sherlock was saying. "How does this help you with your," and he gestured to the still-exposed patch on Lestrade's arm.
It didn't, of course. Or did it? Lestrade wasn't sure, but he did know that he had been awake all night, and now, talking to Sherlock, he felt… warmer, somehow. Less empty. He might actually even be able to sleep, if he tried.
"Maybe I'll get my rush from watching you take apart Anderson's dignity all over the next crime scene," he grinned wryly.
"I can do that," Sherlock replied with great seriousness.
"God help us."

And sleep he did, while his "consulting detective" sat on the couch and flung papers into document boxes with abandon. They could go back to Scotland Yard. He didn't need them anymore. He had the really interesting ones now.

Before he drifted off, though, it occurred to Lestrade that he ought to be laughing at their ridiculous role reversal.

Sherlock Holmes, helping Detective Inspector Lestrade kick his addiction.

Who could possibly have seen that coming?