Mercedes (Marga Lopez) dances for money with the clients of Salón México, a famous cabaret in Mexico City. Her younger sister Beatriz (Silvia Derbez) studies in an expensive private school, paid by Mercedes. Obviously, young Beatriz doesn't know about her sister's job. Troubles begin when Mercedes wins a danzón contest with Paco (Acosta), her pimp. Paco refuses to share the prize with Mercedes, so she steals the money when he's sleeping.