On his first tour of duty in Afghanistan, Sam Brown was set on fire by an improvised explosive device. He survived, only to find himself, like thousands of other vets, doomed to a post-traumatic life of unbearable pain. Even hallucinogen-grade drugs offered little relief, and little hope.

Then his doctors told him about an experimental treatment, a painkilling video game supposedly more effective than morphine. If successful, it would deliver Brown from his living hell into a strange new world—a digital winter wonderland.

At will and sometimes against his will, Sam Brown can return in his mind to that hour in the Kandahar desert when he knelt at the edge of a blast crater and raised his flaming arms to the Afghanistan sky. He’d already run through the macabre slapstick routine of a man on fire, trying to put himself out by rolling on the ground. He’d resorted to pelting his face with fistfuls of sand. That failing, he’d run in helpless circles. Finally he’d dropped to his knees, lifted his arms, and screamed Jesus, save me. Each scream drew fire deeper into his lungs. Behind him his Humvee was a twisted inferno. Bullets whizzed around him. His men were scattering, taking cover, moving dreamily in clouds of so-called moondust, that weird powdery talc, which hung in the air and gave the soldiers the appearance of snowmen. It was going on dusk, and in the fading light the enemy gunfire blazed behind the walls of the village.