After being widowed with a young child, Cristina (Rocío Durcal) must teach languages to survive. One day she is discovered by a young man named Alfonso (Arturo Fernandez), who convinces her to impersonate his missing sister Mara (also played by Rocio Durcal)--to whom she has a remarkable resemblance--to help the mental and physical recovery of his brother Javier (Emilio Gutiérrez Caba), the abandoned husband, who suffers from heart disease. For a time, the masquerade works, but everything gets complicated when the real Mara returns.