Mercedes (Marga Lopez) dances for money with the clients of Salon Mexico, a famous cabaret in Mexico City. Her younger sister Beatriz (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 danzon contest with Paco (Acosta), her pimp. Paco refuses to share the prize with Mercedes, so she steals the money when he's sleeping.