Without further preamble, the three of them went to the back wall, then - he and the doctor and the bassoonist - where Erik set his burden down long enough to trigger the wall mechanism. He was careful to angle his body in such a way that Hannibal could see exactly how to activate the sliding wall. And then they stood before a long and dark stone corridor. Lighting was tricky, in that there was none. He knew his way by memory; he'd designed it specifically so that it was nothing to recall the steps. But Hannibal did not.
"Keep in mind the three-chord progression of a 7th dominant in e-flat," he instructed. "For every note above 'A', walk five steps. Every note below takes ten. At the end of every chord, there is a trap to disarm, which I will show you. Once disarmed, turn left at the top of the first and third, right at the second."
Erik glanced at Hannibal, then took up his portion of the burden and stepped into the corridor, waiting until Hannibal followed to toe the latch that closed the wall again, soundlessly. Darkness fell. Erik let out a sigh. The perfect darkness was a comfort he never had dispelled.