"I'm not leaving you, Sherlock." No amount of self control could hide the exhausted pain in John's voice.

"Idiot. Sentiment will get you killed." Sherlock's response was muffled by the thick door between them, but it did nothing to hide the breathless agony in the other man's voice. The sound made John's chest ache.

"Not by you at least." The doctor tried to be flippant but it was difficult to joke when his best friend was slowly dying not two feet away and he was powerless to even ease the pain. Sherlock gave a snort that dissolved into a hacking cough.

"Only so long as you do not do something incredibly stupid." The detective got his breath back enough to answer but he still sounded raw.

"I can't open the bloody door and I doubt you'll be able to break out of there." Both of their voices were tight even as they tried to carry on something like a normal conversation.

From the other side came a chuckle that broke into rasping coughs yet again. Sherlock wheezed as he tried to draw a breath that didn't end in hacking and slowly the rasping gasps faded into a silence that stretched on like a bottomless abyss.

"Sherlock?" John's question was soft, fear shaking the word. He received no answer.

"Sherlock?!" Panic spiked the name into a yell. In response there was another cough and a groan.

"'M n-not gone yet, John." Sherlock's voice was weak but there was a touch of bitter mirth beneath the words. John slumped back against the door with a thud and a breathless curse on which his voice broke.

"You do know I'm not going to last much longer?" The detective's weak voice held a great deal of resignation. John shuddered.

"I'm still not going to leave you." The doctor's voice was tight and hard.

"Idiot." To anyone else the words was an insult but John heard what almost sounded like an endearment.

"What are you going to do when I'm gone?" Sherlock's voice held a faint note of fear as he tried to keep the silence from becoming crushing.

"I'll keep doing what I've been doing. Surviving. And I'll come down here and tell you about it. No point in trying to keep a blog without the internet." John's voice shook, but they both ignored it as they had been ignoring every bit of pain and weakness and fear the other displayed. Just as John was ignoring the tears he could feel streaming down his face.

Sherlock snorted again and there was a soft thump as he leaned his head back against the door.

"Really John, you should go find other survivors. You're going to go mad talking to the groaning corpse in your basement as if it's still your flatmate." The derision in his voice fell on deaf ears.

"Friend." John didn't hesitate to snap out his correction. The silence that followed felt almost startled.

"Friend then." There was a smile in Sherlock's voice. John's heart ached further at the unusual agreement. His head thudded back against the door with a sigh.

"Best friend really. Closest I've ever had." The doctor's voice was chocking on his tears now. It took a full minute for Sherlock to respond and John almost jumped when he finally did.

"Only one I've ever had, really." The detective's voice trailed off into harsh breaths.

"Sherlock, I..." The rest of John's words were drowned out by sudden racking coughs. The sounds were wet and raw and final.

"Sherlock?!" The doctor surged to his feet, thumping painfully against the door as he did so. His panic was strong enough that he might have gone back on his word and opened the portal, but Sherlock had changed the locks in anticipation. Even as he pounded on the door the coughing subsided again into pained wheezing.

"Sherlock?" John was pleading now, voice breaking as he pressed against the door as if he could pass through it.

"John..." The doctor nearly missed the word, groaned out so faintly in a final breath. Silence fell , heavy and cold with only John's stuttering breaths to break it. He crumpled beneath the deafening quiet, sliding down to kneel in front of the barrier keeping him safe from the monster his friend's corpse would shortly become.

How long he knelt before Sherlock's tomb and prison he didn't know. Enough time passed that his tears ran dry. Enough time passed that the discomfort in his knees forced him to shift, sitting so that his back was against the door once more. Enough time passed that the virus that had killed Sherlock worked its final devastating change.

The crushing silence was broken by a rattling inhale, followed a minute later by an exhale that groaned out of a dead throat. John winced and took his own breath as the undead mockery of life shifted about in the dark on the other side of the door.

"I remember when we first met. You were standing with your nose in a microscope in a lab in Bart's. You'd just come from the morgue, where you'd apparently left your riding crop." The attempt at lightheartedness fell flat. He hesitated, listening a moment to the shuffling, uncoordinated movements.

"Never did ask why, wasn't sure I wanted to know. 'Course, now I think about it you were studying bruising patterns." He swallowed thickly as nails scraped lightly against the door.

"I thought you were a student at first, given how you looked." He continued talking until he was hoarse and exhausted. All the while the animated corpse on the other side pawed at the door, groaning in and out, useless breaths that rattled through undead lungs.

At long last the words ran dry. John hauled himself upright on shaking legs.

"Goodnight...Sherlock." He choked on the final farewell he hadn't been able to give when Sherlock had been taken from him. The creature behind the door stilled at the softly spoken words.

Silence followed John as he checked the lock on the door and climbed the stairs to the ground floor. Silence crushed him as checked the locks and barricades on the ground floor. Silence nipped at his heels as he climbed the narrow stairs and locked and reset his trip lines. Silence tore great holes in his soul as he locked the door of 221B Baker Street behind him and stared into the empty flat.

Sleep did not come to John Watson that night.