Shy, timorous bank clerk, Fernand Jérôme, prevents -unwillingly of course - a gang led by "Le Grand J" from robbing the "Crédit Populaire", where he works. Having become a hero out of the blue, this new status allows him to woo Renée, the daughter of chief inspector Merlerin. What Merlerin does not know is that the man he has been trying to arrest for years, "Le Grand J" is in fact Joseph Jérôme, Fernand's father, who has disappeared for years...