Just before the Bastille Day holiday weekend English secretary, Danielle "Dany" Lang, types up a document for her advertising agency boss, Michael Caldwell, to take on a business trip to Geneva. On the way to drop off her boss and his wife, Anita, her former room-mate, at the airport, her boss gives her an envelope with her pay in it.
After dropping them off Dany impulsively decides to drive to the Riviera for the weekend. When Dany pulls into a small café the owner tries to return a coat to her she claims she left there the day before. At a petrol station Dany is attacked in the toilet and injures her hand. She is bemused as various strangers claim to know her.
Heading further south she picks up a hitch-hiker, Philippe and the pair spend the night together. The following day Philippe steals Dany's car prior to reaching the coast. She later finds Philippe in Marseilles where they find a man's body and a gun in the trunk of the car.
After Philippe disappears again, Dany visits the home of the dead man in Avignon and oddly finds both some of her clothes and also nude pictures of herself. Returning to the café to reclaim the coat she finds a copy of her pay envelope in one of the coat's pockets. Dany is now completely perplexed by the situation and returns to the dead man's home where her boss, Michael, is waiting for her. He tells Dany that the dead man was one of Anita's lovers, whom she murdered at his home. To frame Dany, they planted evidence and set up various incidents to establish her guilt: the attack in the toilet was committed by Michael, who injured her hand so Anita could wear a bandage and be mistaken for the secretary; and the nude photos had been taken by Anita when they were roommates.
When Michael tells Dany he plans to murder her and make it look like a suicide she tells him he won't succeed as she has already sent both pay envelopes to the police.
