Marc and Hans, two old gangsters, are ordered by a rival, the American woman, to repay a debt. They plan to steal the vaccine for a mysterious virus, STBO, which affects those who make love without being in love and is wreaking havoc among teenagers. After the death of their associate Jean the two accomplices call on his son, Alex known as "Chatterbox", who is a talented conjour. Alex, who has just left his girlfriend Lise, falls madly in love with a girl in a white dress he sees on a bus. Her name is Anna and she turns out to be Marc's mistress.