La desconocida tells the story of a woman (Ana Rujas) found by the police inside a container in the port of Barcelona. Unable to remember her identity, they take her to the hospital, where her life is once again in danger after an attempted murder. Detective Anna Ripoll (Candela Peña) is assigned to investigate this enigmatic case alongside Officer Quique Zárate (Pol López). Together, they embark on a race against time to discover the identity of this mysterious woman and the secrets hidden in her memory.