Professor Poponof, an old scientist, has just discovered a truth serum. Amédée, a burglar who has been surprised in his apartment, will become the perfect guinea-pig for testing the prof's last find. And it works well. Too well in fact, for if Amédée tells the truth he tells it to everybody and in every circumstance, thus causing disasters around him.

A girl, Marie, who got engaged to a boy who is leaving for military training (thirteen days) wins two million on the raffle, thanks to an older man, Claude, whom she calls her good luck …