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.