***

The gray machine took nearly a minute to boot. Its tiny cooling fan rattled against a metal grille. Evelyn fed the USB into an adapter and clicked a switch marked DEMO ONLY. A low grid appeared on the screen, each small square representing a portion of the moving floor.

“Run the safe sequence,” Mara suggested.

Evelyn pressed a button. The grid lit up in a wave of white squares. The virtual floor lowered gently toward its resting position. Then a red square flashed near the center, followed by a second and a third. The display froze.

ERROR: PHASE CONFLICT.

“That’s what happened,” Evelyn said. “The floor tried to lower and rise at the same time.”

“Was it a programming error?”

“That was Peter’s conclusion.”

Mara leaned closer. Along the side of the simulator was a little wheel with twenty-four marked positions. She rotated it. The simulation restarted at a different frame. The same failure appeared, but this time she noticed something peculiar: the red warning didn’t begin where Alicia had been standing. It began near the control connection, before propagating across the platform.

“Can we slow it down?”

Evelyn hesitated. “That’s the slow setting.”

“I mean one input at a time.”

They spent twenty minutes learning the machine’s awkward controls. Mara found a service mode Evelyn had forgotten existed. It allowed the simulator to display which input had triggered each motor.

When they replayed the failure, the screen showed an ordinary lowering command. Then another command arrived from an unlisted source.

INPUT 05: EXTERNAL SHOW CONTROL.

Mara frowned. “There were four keys.”

“Exactly.”

“What’s input five?”

Evelyn reached for the screen as if she could pull the words out.

“There was no input five,” she said.

Mara didn’t speak for a long time. They ran the sequence twice more. Each time the external command interrupted the safe position, making a different group of virtual panels snap upward.

“Peter didn’t write a bad emergency program,” Mara said. “Something overrode it.”

Evelyn rose unsteadily and began opening drawers. She searched for a thick instruction manual, found it, and leafed through pages marked with pencil corrections. The controller diagram showed four inputs, numbered one to four, and an unused expansion port.

“Who had access to that port?” Mara asked.

“Peter. Me. Gabriel when he helped with wiring. A few apprentices.”

“Was Julian one of them?”

Evelyn stopped turning pages.

“He was fourteen,” she said. “He came every Thursday to help with lighting.”

Mara looked at the photograph of the original workshop pinned above the bench. There, at the edge of the group, stood a narrow-faced boy with a box of colored bulbs. He wore a jacket that was too big for him.

“Did he connect the lights to the moving floor?”