Barcelona, summer 1909. When the scientist and explorer Randolph Foulkes is blown up in a random terrorist bomb attack, private detective Harry Lawton is hired by the man's widow to identify the beneficiary of a large payment Foulkes had made shortly before his death. Lawton's arrival in the Catalan capital coincides with a series of unusual killings that appear to have been carried out by a blood-drinking animal in the Ramblas district and adds another element of instability to a city already teetering on the brink of insurrection. Lawton soon meets and teams up with Esperanza Claramunt, a young anarchist whose lover was one of the victims of the "beast of the Ramblas," and the Catalan crime reporter Bernat Mata, who has begun investigating these crimes.

So what begins as a straightforward investigation into presumed marital infidelity turns into something far more sinister, as Lawton probes Foulkes's connections to the mysterious Explorers Club, the Barcelona political police, and an eccentric Austrian hypnotist. Adrift in a city gripped by rebellion and lawlessness, Lawton enters a labyrinth of murder, corruption, political conflict, and crazed racial pseudo-science where no one's survival is guaranteed.