Ernesto and Marta, a couple of newlyweds who have serious financial problems, are visited by a neighbor asking them to keep a large sum of money at home until she goes to the bank the next day.

Once Upon a Time, one of the first animated films made in Spain, is a free adaptation of the story Cinderella by Charles Perrault. It was directed by Cirici Pellicer, pseudonym of Jaime Baguña Gil, and obtained recognition for the best children's film at the Venice Film Festival.