Cristina ( Rocío Durcal ), after being widowed with a young child, has to 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) - with who she shows a remarkable physical resemblance - and in so doing 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 makes an appearance.