Mika (Isabelle Huppert) inherits a gloomy mansion near Lausanne after marrying André, (Jacques Dutronc) a concert pianist and recent widower with a son, Guillaume.

Jeanne (Anna Mouglalis), a young beauty, turns up on their doorstep with a story that Guillaume and she may have been given to the wrong families following a hospital confusion at birth. She is a talented pianist and soon André is tutoring her as a protegée.

After Jeanne discovers that some hot chocolate prepared by Mika for Guillaume has been heavily spiked with a sleeping drug, there is a suspicion that André's wife may have died following a similar concoction prepared by Mika.