A middle-aged man, an architect by trade, decides to make an end run around getting married. He marries a charming young woman, tenderly in love, who proves incapable of holding him back and, above all, of making him work. But a young American arrives in Paris and reveals that he is the architect's natural son. At first reluctant, the latter and his young wife quickly adapt to the new situation, until the son, a businessman through and through, wants to share with his father his ideas on life, which can be summed up in one sentence: hard work, with no time for pleasure. The father is quick to balk, and the son is forced to unwillingly participate in the fickle architect's nightlife. Eventually, the father is able to settle down, while the son, having acquired a taste for love, has a good time.

The fictionalized life, and interpreted by himself, of the popular boxing champion Marcel Cerdan. Training sessions, matches, victories, flight to the U.S.A. where the title of world champion is disputed, form the whole subject of the film.