A call from Rodney halted him. "Back here," the tall man repeated. "It looks like a switchboard."

The three advanced to the end of the central corridor, pausing before a great arch, outlined in the too-careful geometrical figures Martin had come to associate with the city builders. The three torches, shining through the arch, picked out a bank of buttons, handles ... and a thick rope of cables which ran upward to vanish unexpectedly in the metal roof.

"Is this it," Wass murmured, "or an auxiliary?"

Martin shrugged. "The whole city's no more than a machine, apparently."

"Another assumption," Wass said. "We have done nothing but make assumptions ever since we got here."

"What would you suggest, instead?" Martin asked calmly.

Rodney furtively, extended one hand toward a switch.

"No!" Martin said, sharply. That was one assumption they dared not make.

Rodney turned. "But—"

"No. Wass, how much time have we?"