Arthur Bryant and John May—and their team of proud eccentrics in the Peculiar Crimes Unit—have been given only one week to hunt down a murderer they’ve already caught once, but who somehow escaped from a locked room and killed one of their best and brightest. Facing a shutdown, Bryant and May, men of opposite methods, learn that their nemesis, expertly disguised, has struck again—and now he is luring them down into the vast labyrinth of tunnels and dark shadows of the London Underground. But soon they will discover a fresh mystery—one as bizarre as anything they have ever faced.