A series of brutal murders linked to a mysterious ancient tree plunges the city into a supernatural crisis. Detective Constable Peter Grant, a probationary constable with the Metropolitan Police, finds himself drawn into a world of magic and the supernatural as he investigates a string of gruesome killings. The victims are found drained of blood, with strange symbols carved into their bodies, and the only common link appears to be a connection to a legendary, possibly sentient, ancient tree. Grant must navigate the treacherous waters of London's magical underworld, facing off against ancient evils and internal police skepticism, all while trying to solve the murders before the city succumbs to the darkness emanating from the Hanging Tree.

The PC Grant series is generally well-regarded for its unique blend of police procedural and urban fantasy, with 'The Hanging Tree' continuing this trend. Critics often praise Aaronovitch's witty prose and his intricate world-building, which grounds the magical elements within a realistic London setting. Readers appreciate the character development of Peter Grant as he grapples with increasingly complex magical cases and his own limitations. The novel is seen as a solid entry in the series, offering both thrilling mystery and engaging supernatural elements.