His footsteps rang down the hallway in quick succession. Even though he could hardly see the floor in front of him, Mark could hear the footfalls to the rear, gaining. Adrenaline rushed through his veins, but his leg muscles were beginning to cramp.

“I can’t keep this up,” he wheezed in a panic. “I’m dead.”

As if to underscore the point, more echoes emerged from the darkness—grimy sneakers, tattered dress shoes, and heavy, labored breathing. The night terrors were closing in with a speed and singlemindedness that belied the fact they’d once been human.

A stitch had been growing in Mark’s side, and at this crucial juncture it flared up, joining his legs in demanding an immediate and unconditional rest. “No…” Mark said. “Don’t you understand…you worthless…appendages? If I stop…you die!”

Despite this exhortation, he continued to slow. Moments later, he felt the first probing fingertips on his back and neck.