Pain.

  Not the familiar kind — not the lower-back ache from twelve hours in an office chair, not the sharp specific protest of a stubbed toe. This was systemic. Every nerve reporting simultaneously, like an orchestra tuning up: discordant, formless, each instrument screaming its own frequency with no conductor in sight.

  He tried to categorise it. Old habit. Sort the data, find the pattern, reduce the noise. The pain was concentrated in his chest — no, deeper than his chest. In a location his anatomy courses had not prepared him for, somewhere behind his sternum and below his diaphragm, in a space that felt like a room with broken furniture. Something inside him was shattered, and the shards were vibrating.

  He opened his eyes.

  Dust. Brown, fine-grained, suspended in air that smelled of copper and something older, something that reminded him of the mineral collections in the Stanford geology building — millennia compressed into a scent. He was lying on packed earth. The sky above was the colour of a healing bruise: yellow at the edges, grey-purple at the centre, with no visible sun.

  He sat up and immediately regretted it. The shattered thing in his chest shifted, and for a moment his vision went white with a pain that had no analogue in his experience. He breathed through it. Catalogued it. Filed it under "internal anomaly, cause unknown, severity high."

  His hands were wrong.

  He stared at them for eleven seconds — he counted, because counting was what he did when the world stopped cooperating — and confirmed that these were not his hands. His hands were forty-three years old, with a burn scar on the left index finger from a soldering incident in graduate school and fingernails bitten to the quick because Elena had never successfully broken him of the habit. These hands were young. Smooth. The fingers were longer than his, the skin a shade darker, and there was not a single scar on them.

  He conducted a systematic inventory. Two arms, functional but weak, belonging to a body perhaps twenty years younger than the one he remembered. Two legs, same assessment. A torso that ached in unfamiliar proportions. A head — his head? someone's head — with hair that fell past his ears, which was disorienting because he had been balding since thirty-six and had made his peace with it.

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  And the broken thing in his chest. The shattered room. He pressed his palm against his sternum and felt the vibrations of whatever had been destroyed in there, each fragment oscillating at its own frequency like a smashed crystal still ringing with the memory of its original note.

  He stood. The landscape resolved.

  Bones.

  He had expected rocks, or trees, or buildings — some structure that would contextualise his situation, place him in a geography he could navigate. Instead: bones. Not scattered remains, not the casual disorder of natural death. These were arranged. Rows upon rows of skeletal figures, some still wearing armour that had corroded into lace-like patterns of rust and verdigris, positioned in formations that suggested military discipline maintained long after the muscles that enforced it had dissolved. A battlefield. Ancient. Enormous. Stretching to the horizon in every direction, so that the brown earth he was lying on was not earth at all but the compressed sediment of tens of thousands of the dead.

  He was standing on a mass grave.

  The physicist in him — and it was still the largest part of him, the load-bearing wall of his identity, the thing that remained when everything else was subtracted — noted that the bones exhibited unusual properties. Some glowed faintly. Others seemed to repel the dust that settled on everything else. A femur three metres to his left was warm to the touch, as though something inside the marrow had not yet finished dying.

  He picked it up. It weighed what a femur should weigh — he had handled bones in an undergraduate anatomy elective, a requirement he had resented at the time — but there was something else. A faint, rhythmic pulse, not physical but... adjacent to physical. Like a sound below the threshold of hearing, or a colour outside the visible spectrum. His instruments would have detected it. His body, apparently, could detect it too.

  He held the bone and counted the pulses. Regular. 0.73 seconds apart. He set the bone down and picked up another. This one pulsed at 0.91 seconds. A third: 1.14 seconds. Different frequencies. He arranged them in order and looked for a pattern.

  The pattern was obvious. The pulse frequencies correlated with the apparent age of the remains. Older bones, more degraded armour, slower pulses. Newer bones, better-preserved equipment, faster pulses. Whatever energy the bones contained was decaying over time. Decaying at a rate that, if he had a clock and a notebook, he could quantify.

  He did not have a clock. He did not have a notebook. He had a broken body, a shattered something-in-his-chest, and a mass grave.

  He began counting.