Mr. Pierre Montabrel has spent all the night with his mistress.On the morning Gisèle Montabrel, his wife, is preoccupied because Pierre is not at home.Then arrives Jacques Lambert, the associate of Pierre, Gisèle asks him if he has worked with Pierre in the office at night, but Jacques Lambert answers that that he just came back from Bruxelles.Some minutes later Gisèle and Jacques are observing that Pierre has arrived and has gone to his bedroom.So Gisèle becomes angry and asks Pierre about what he has done in the night.Pierre answers that it's personal.Gisèle gives him an ultimatum, within two hours he must tell her the truth.Pierre sees in front of his house a private detective agency, he calls there explaining his case (he needs an alibi).Sometimes later Mr. Tellier ,manager of agency, arrives with a man, Mr. Robert Crémieux who will play the role of an old school friend that Pierre met in bar at night , they talked about their lives and drank a lot to champagne and finally Robert carried home Pierre at 6 a.m. Robert Crémieux is also happy to make that deal because he needs also an alibi for personal reasons.