Northern Spain, October 1944. Several groups of guerrilla fighters, former Republican soldiers exiled in France after the end of the Spanish Civil War, infiltrate the country in order to provoke a popular uprising against General Franco's dictatorship.

A soldier from the 15th century, a university student from the 19th century and a nurse from the present join the secret 'Department of Time', a secret department within the Spanish government with the ability to travel through time. Their mission is prevent changes in history.

Recounts the experiences of a middle-class family, the Alcántaras, during the last years of the rule of Francisco Franco and the beginning of the Spanish Transition to democracy.