For years, Elias had been haunted by a memory: a silver-haired man giving him this very notebook when he was just a boy. "The world ends in fire," the man had whispered. "Unless you build the Machine."

Elias stood in the ruins of the Great Library, clutching a charred leather notebook. He was a "Time-Sensitive," capable of feeling the hum of a —a point where time tracks diverged and collided.

In a panic, Elias realized the "fire" the man spoke of was the very act of building the machine. He grabbed the notebook and stepped through the shimmering portal.