A cryptic message left by a dying man plunges London's Peculiar Crimes Unit into a baffling investigation. Arthur Penhaligon, a man with a past shrouded in secrets, collapses in a London street, uttering only a string of seemingly nonsensical numbers. Detectives Bryant and May are tasked with deciphering this code, which leads them through a labyrinth of hidden histories and dangerous conspiracies. They must unravel the invisible threads connecting Penhaligon's final moments to a shadowy organization with a deadly agenda, all while navigating the complexities of their own partnership.

Bryant & May and the Invisible Code is generally well-received within the context of Christopher Fowler's long-running detective series. Readers familiar with the characters of Bryant and May appreciate the continuation of their unique partnership and the blend of quirky humor with intricate plotting. The novel is noted for its clever use of historical detail and its ability to weave a complex mystery that engages both the intellect and the imagination. The series is praised for its consistent quality and its distinctive voice, making this installment a satisfying entry for its established fanbase.