Monsieur Monde manages an important transport company and leads a simple, regulated, quiet and rather uneventful life. Then, on his 48th birthday, without any warning, he gives it all up, packs his bags and gets on the first train to Marseille. On arrival, he wanders around helplessly until he meets a girl who changes his view of life completely. A sensitive film, taken from the eponymous novel by Georges Simenon, about a theme that continues to be current: what propels some people to leave the everyday behind and throw themselves into life, headfirst?