A controversial artist is found dead in her own art installation inside a riverside gallery with locked doors and windows - the only witness is a small boy who insists the murderer was a masked man on a horse. A television presenter is struck by lightning while indoors... Two seemingly impossible crimes that only Arthur Bryant and John May of the Met's Peculiar Crimes Unit might be able to solve.

But Bryant has lost his nerve following a disastrous public appearance, and May is fighting to keep the unit from closure. Worse still, the case of the Leicester Square Vampire, an unsolved mystery from the past that changed both their lives, has returned to haunt them. With a sinister modern-day highwayman bringing terror to the London streets in a series of crimes each more puzzling than the last, the elderly detectives track their suspect to an exclusive private school and a deprived housing estate.

But just when they need all the help they can get to uncover a new breed of criminal, the highwayman is hailed a national hero, and the public turns against them... Bryant & May are back on the case in an adventure that explores the dark side of celebrity, the conflicts of youth, age and class, and the peculiar myths of old London.