Fernand, a simple employee at the Prefecture of Police, must serve as a "sheep" to extract confessions from a leader of organized crime, who has recently been in prison. But he managed to escape by taking Fernand hostage.

Fernand is a model employee of the Prefecture of Police. Her only ambition: to marry the lovely and delicious Gisèle Martin, daughter of her landlady. One day, the commissioner decides to send him to prison, to make the "sheep", that is to say, spy on his fellow prisoners and more particularly the Tiger, head of organized crime who has just been arrested. But the Tiger escapes and takes the brave Fernand hostage.