They kept the seat beside him on the plane empty. He knew Mycroft was behind it, and really he was grateful; the last thing he wanted when he was flying away from everything he'd ever cared about was to have to sit next to some narrow-minded plebeian who wouldn't understand why he was crying.

After a while, he had to acknowledge that Mycroft had probably anticipated the talking as well. John – bless him – was constantly telling people that Sherlock talked to him even when he wasn't there. And his elder brother always understood better than he did that people don't particularly like being constantly addressed by someone else's name, especially on long flights.

He couldn't help it. He knew John didn't understand, not really. It wasn't because he just didn't notice that John had gone out; Sherlock talked to him because he needed him there, even when he wasn't, and in those moments when he wasn't it felt sort of empty somehow until he was driven to fill the silence with empty words.

Like now. Sherlock didn't think he'd ever felt this empty before, and as a result, there were more words needed to make the silence feel slightly more bearable.

"I'm really sorry, John."

The empty seat beside him didn't reply. He watched it for a moment, but it didn't get any more forthcoming, so he sighed instead. "I understand if you don't want to talk to me. I wouldn't want to talk to me either. I feel terrible. But… I didn't have a choice, John, you have to believe me."

The woman across the aisle looked over at him strangely. He looked back with deep mistrust. "People are staring at me," he said idly. "They think I don't realise you're not here.

"Oh, John. You should have believed what I told you, you know. About me being a fraud. This will be easier for you if you hate me. Especially if I…"

Even though he knows he's just talking to himself, it's hard to say. He clenches his fists until they almost bleed; for some reason the pain makes it feel better. Physical pain, to blot out some of the guilt. "Especially if I don't come back.

"No. That's stupid. I will come back, John. I miss you so much I can't breathe, already. Three years. If I haven't caught all of them in three years, I'll come back anyway and you can help me. If I can't catch all of them in three years, it'll be the final proof that I can't work without you." He chuckled slightly to himself. "I miss you already," he said gently. "You'll probably never know how much. I should have told you, but I was always too proud. You're the only friend I've got – I always wanted you to think well of me so you'd never leave."

For a while he considered sleeping, but it only led his thoughts back into the loop that consisted only of the guilt – he was my friend and I hurt him – and his own sense of loss – he's my friend and I have to re-learn how to live without him.

"John?" he ventured after a while. There was no answer. "Do you remember that time you were dreaming about Afghanistan again and you came downstairs and I sat next to you while you fell asleep? No, probably not. Actually, I don't think you knew I was there at first, but I was worried about you. I'm sorry. I watched your eyes struggle to close for a while until you'd be almost asleep, and then the dream would start again and you'd jerk awake… until I went and sat beside you."

He looked up to try and hold back the tears, but it wasn't any use. "John, I… I need you to be okay with this. Well, no, not okay, but you know. You're the strongest person I know and I need you to be strong now as well, because one of us has to be strong when I come back, and I… I can't. I won't be able to. I'll want you to sit beside me while I fall asleep crying because I've missed you."

A stewardess wandered past and asked if he was all right; after that, he weathered the flight in relative silence.

"John, pass me my phone."

It took fourteen months before he stopped expecting anyone to respond to his requests, but he never stopped making them. In time, "John, pass me a pen" became "John, I'm sorry, but do you think you could please pass me a pen?" but it didn't help. He didn't really expect it to.

He kept talking, though, because to stop – no matter how stupid it seemed – would feel like admitting defeat, forgetting John, and he never wanted to do that. They were just little things, like "John, could you put the kettle on?" or "Are you hungry, John? Shall we get dinner?" or, in one memorable occasion, "John, you'll want to bring your Browning on this one, I might need you to watch my back."

On that occasion, the Russian assassin had turned hostile and Sherlock had wound up almost getting shot. In fact, he was so close to being shot that the bullet actually grazed his shoulder and he'd ended up in A&E, being stitched up by some doctor he didn't know who completely misunderstood the reason he was crying.

It was his left shoulder. He appreciated the symmetry.

For some reason, it felt somehow necessary to rehearse what he would say when he came home; how he'd apologise, and explain, and lay everything out at John's feet - how he'd done it to save him, because he couldn't let John die for him even though he wanted to - and he made allowances for the fact that he knew he wouldn't be able to stop himself from crying. John would probably punch him at some point, but that was fine. He had it coming.

In the end, it was two years, eight months and twenty-one days before he tracked the last of Moriarty's gang – the sniper, Colonel Moran – to London and shot him in an empty house surrounded by the pieces of his long-range sniper.

He'd meant to wait, meant to get a haircut and change clothes and make himself presentable, but instead he staggered the two blocks to Baker Street on foot with the Beretta still in his hand. It would have been faster – and easier on the ankle he'd damaged sprinting down the stairs – to call a cab, but somehow he felt like this was something he had to do manually, had to feel every step of the way because it was important.

He'd caught a glimpse of his appearance in the window at Speedy's and tried hurriedly to flatten his hair and straighten his scarf and – oh, God – brush some of the blood from his shirt before he knocked on the door. Actually, he didn't know if John still lived here. But someone had to.

Mrs Hudson opened the door. Sherlock smiled awkwardly. "Mrs Hudson," he said quietly. "Long time, no see."

It was pathetic and feeble and really not appropriate for the situation, but she squealed and threw herself on him anyway, pulling him inside and engulfing him in a bone-crushing hug. He hugged her back, breathing in her motherly, warm smell, like biscuits and PG Tips. "Oh, Sherlock," she said into his coat. "We've missed you so much."

He hugged her tighter and fought back the tears. Not yet – he couldn't cry yet. "Is he here?" he asked, and she didn't need to ask who he meant.

"John!" she called up the stairs, her voice wavering with tears and frantic, and he felt so guilty all over again for leaving them. "John!"

The door upstairs crashed open and John's voice echoed down the landing. "Are you all right, Mrs H? What's happened? Shall I –"

Sherlock looked up, holding his breath because it felt easier to control himself that way. And there was John, standing on the landing, white as a sheet and breathing like he'd seen a ghost. "Sherlock?" he breathed, stepping down the remaining steps with an almost ethereal calm. And everything he'd rehearsed so carefully, everything he'd said to John when he wasn't there, felt so insignificant that it crawled out of his head in shame.

Eventually he had to take a breath, and once he had relinquished that control over his body the rest of him fell over the edge too, and suddenly he was sobbing and rushing forward and pulling John into his arms, hugging John, feeling John there, drowning in his John smell and his little gasping breaths and murmurs of SherlockSherlockSherlock, only barely aware of Mrs Hudson smiling at him and retreating into 221A."John," he breathed into the sandy, pomegranate-smelling hair. "I missed you, John."

"I missed you, too," John replied fiercely, hugging him so hard he could hardly breathe and it felt wonderful. "You stupid git," the doctor added, drawing away. "I've thought – I spoke at your funeral! How could you just let me think you were dead for three years?"

He knew John was angry, and really he couldn't blame him. He was angry too. "Two years, eight months, and twenty-seven days," he corrected. John's fist collided with his cheek.

He'd been expecting it, and God knows he deserved it, but it still hurt. "Ouch!" he cried, his hand flying to his face. "John!"

The doctor glared at him, but he could see the beginnings of a supressed smile twitching up the corners of his mouth. "Don't try and tell me you didn't deserve that."

He nodded, trying to look humble. "I deserve worse than that," he admitted, flinching in case John took that as a hint and tried to hit him again, but the doctor didn't move. "I'm really sorry, John."

John glared at him for a moment more, then nodded factually. "I know. It's all right." The breath left Sherlock's lungs again, replaced by pure, blind happiness. He was back, finally, completely. He was home.

"Come on, I'll get you some ice."