He had to get moving. He had to get away. Fire engines were coming. He was afraid he would pass out. But a second explosion blowing glass from more windows galvanized him with the realization that the fire was spreading so fast that if Isaac Bell somehow did manage to reach the roof ahead of the flames, he and his bride’s only way down was to jump to the life net.

The Acrobat’s sudden laughter lanced pain through his face, but he couldn’t help it. It was such perfect justice for all Bell had done to him. With Bell’s own knife, he slashed the ropes that held the net.

WHITE SMOKE SEEPED INTO THE secret stairwell. The acrid, tarry stink of nitrate gas clawed at Bell’s lungs. As he raced by the film exchange, a judas hole cover blew open and hot flame shot through the spy hole like a fiery arrow. Bell ducked it and kept climbing, bounding three steps at once, pursued by smoke and fire. He passed the opening to the recording studio. The fire was there ahead of him, licking the bodies, having leaped up an elevator shaft or another stairway, and he prayed that Marion had not left the temporary safety of the rooftop studio in a doomed attempt to descend.

At the fifth-floor landing, when he was halfway to the top of the building, the flames feeding on the hundreds of reels in the film exchange far below breached a vault and detonated tons of film stock stored inside. The explosion shook the stairs under Bell’s feet. A shock wave traveled up the shaft and lofted him off the rubber treads.

He tumbled down half a flight of stairs, clambered to his feet, and ran harder, climbing past Irina’s office on the seventh floor, Clyde’s laboratory on the eighth, and Semmler’s lair on the ninth. After one more flight he was at the top, gasping for breath and stymied by walls on every side. He yanked open a judas door and saw a studio stage in semidarkness, with a looming shadow of a ship and towers bearing Cooper-Hewitt light banks. Silhouetted against a lurid sky, Marion was stepping through the door in the northern glass wall, climbing out on the terrace that overlooked the life net.

Bell shouted. The wall was thick, and she could not hear him.

Remembering the sliding fourth-floor wall, he spotted the bulge where the wall thickened to make room for the pocket. He looked for a lever but saw none. He flattened his palms against it and tried to slide it, which had no effect. Then he saw what looked like an ordinary electric light switch on the floor molding. He moved it and the wall glided aside.

“Marion!”

A second explosion rocked the building.