As it had happened before, a body appears on the first night of the Carnival. The locals are sure this the work of "Urco", and that more murders will follow until the festival is over.
The story is set in Néboa, a fictional island off the coast of Galicia. The corpse of a teenager appears during the first night of the entroido carnival in Néboa. The murder mimics the pattern of past killings that occurred in 1919 and 1989, both of which sparked a serial killing row with multiple deaths. Locals believe the killer is the Urco, a wolf headed man from the folk stories. Three Guardia Civil agents, Mónica Ortiz, Carmela Souto and Lieutenant Ferro try to solve the mystery and avoid another serial killing rampage.