Roman de gare

The successful novelist Judith Ralitzer is interrogated in the police station about the disappearance of her ghost-writer. A serial-killer escapes from a prison in Paris. A missing school teacher leaves his wife and children. In the road, the annoying and stressed hairdresser Hughette is left in a gas station by her fiancé Paul while driving to the poor farm of her family in the country. A mysterious man offers a ride to her and she invites him to assume the identity of Paul during 24 hours to not disappoint her mother. Who might be the unknown man and what is real and what is fiction?