Lestrade was likely one of the first though they never learned for sure. Scotland Yard had tried to keep order and prevent panic before the military finally admitted the problem and made a move. By then it was too late. Far too late.

John was lucky, not working the day it began, and the next, when the strange news hit, Sherlock forbade him to leave. John had scoffed, of course, and tried to leave anyway. He woke up with a pounding headache and handcuffed to his sturdy bed frame. Sherlock had been kind enough to leave him some aspirin and several bottles of water. He, however, was not nice enough to leave his phone within reach. It sat mocking him across the room on his dresser.

John wasn't sure how much time passed when the screaming started: horrified, panicked, desperate, filled with pain and misery. It was the worst of Afghanistan all over again, and John struggled until his wrists bled, until the screams finally stopped, cutting off in such a way that could only mean one thing. As the sun set and silence continued to reign, that was the worst of all.

London was never silent.

At some point John slept, for how long he wasn't sure. The soft sound of his door opening woke him and set him instantly on edge. Making out the silhouette of Sherlock through the dimness of the room, John instantly relaxed as though a weight had been lifted from his shoulders, having imagined the worst in the long hours of the past day.

Sherlock lowered the shade and pulled the curtains over the window before flipping on the bedside lamp. For a moment, John wavered between fear and anger, but finally settled on despair as he noted the pinched look Sherlock wore. Weary and exhausted, it was the closest to alarm that John had ever seen Sherlock express.

It wasn't a good thing.

"John," Sherlock whispered, the soft sound, but almost too loud, a prayer, an apology, the one word trying to express so many things. He made quick work of John's bindings, cleaning and bandaging his damaged flesh, Sherlock's touch soft and remorseful.

The silence was oppressive, heavy around them, and John feared breaking it. When Sherlock spoke again, John couldn't help but jump.

"It shouldn't be possible. It defies all logic and goes against basic biology. It's like something from a bad horror film," Sherlock paused, his skin far too pale, making the flush along his cheekbones stand out in shockingly stark contrast.

"Tell me," John prodded, tugging Sherlock down to sit beside him on the bed even though a part of him really didn't want to know.

Sherlock's words were soft and rapid. "Immortality. But not the kind alchemists have sought for millennia. This is a twisted parody, a blight against the basic laws of nature. Cells stop dying, but they stop multiplying as well. Higher brain function quickly fails, taking with it emotion and rational thought until finally there is nothing left but hunger. They don't stop; they don't sleep. Nothing short of incineration can slow them for long."

"Zombies," John breathed in disbelief.

Sherlock nodded, silent and drawn, and John laughed, soundlessly, hysterically until he was too exhausted to think. It was too crazy to comprehend, but it was happening. They didn't speak for a long time, just sat pressed against each other's sides, supporting each other in a world that had gone askew.