Mr Jo, nicknamed "the man with the Buick", is the darling of the small town of Honfleur. But he is in fact a trafficker with a bad reputation who would like to forget about his past, now limiting himself to smuggling rubies under the cover of a charitable organization which offers underprivileged children holidays in Switzerland. However, Mr. Jo is in love with a pretty widow and, in order to marry her, he is willing to get involved in a hold-up again. And "the man with the Buick", who seemed so honourable, will surprise the inhabitants of Honfleur when Inspector Menard reveals his secret activities.