They timed the switch to the chorus of a distant train; Arjun’s hands, a blur, traded books in a single heartbeat. The ledger was lighter than it looked. For a breathless second, the world shrank to the thrum of cables and the tick of a clock. Then an alarm — not theirs — blared. A guard, who’d sensed a wrong note in the janitor’s mop-song, kicked open the door.