A Spanish diplomat falls from the top of the Águas Livres Aqueduct. The PJ (Portuguese Judicial Police) investigates with the help of a Spanish inspector, quickly concluding that there is a serial killer in Lisbon, inspired by the legendary "Aqueduct Killer" of the 19th century: Diego Alves. Just when the police seem close to solving the case, a twist reveals that the psychopath is still at large, this time driven by personal revenge.