Mika, heiress to a Swiss chocolate company, is married to celebrated pianist André and stepmother to his son, Guillaume, whose mother died in a car wreck on his tenth birthday. Their lives are interrupted by the unexpected arrival of Jeanne, a young woman who has learned she was almost switched with Guillaume at birth.

A young woman falls down a staircase, and suddenly becomes... a nymphomaniac.

After a successful experiment on Algernon, a mouse whose level of intelligence thanks to that procedure dramatically increased, the scientists decided to go further - the next "guinea pig" is Charles, a mentally disabled young man. The experiment is again successful. But what happens after it?