While celebrating his birthday, police inspector Basquier recalls two of his most celebrated cases. The first involves duplicitous moneylender Olga. The second concerns the brutal broad daylight murder of innocent young Yvonne.

Noël is a bachelor who inherits a matrimonial agency. After contemplating selling it, he chooses to manage it.

Due to financial problems, the boarding-school of Saint-Loup is on the verge of closing its doors. In desperation, Jacquelin, the headmaster, has the idea to invite former students to a fund-raising reunion. Among the alumni, three men whose common point is to have been in love at the time with the headmaster's niece. One is a banker, the second a priest and the last one a globetrotter. All of a sudden, the peace of the assembly is disturbed: Jacquelin's niece has just been murdered.

Louis Mennechain is a modest locksmith. So imagine his amazement when Professor Piétrefond approaches him and tells him he recognizes in him a descendant of the kings of France, more precisely of Louis XVII (the king who never reigned). According to him he is none other than the monarch's great grandson. Louis's life is soon turned upside down as he becomes the center of attention of a group of ardent royalists. Even a duchess "gives" him her love to make sure that he accepts his role as pretender to the throne...