Antoine Derouere (Jalil Lespert) completes his education at the Police Academy and heads for Paris to join the Second Division of the Detective Branch. Caroline Vaudieu (Nathalie Baye) is back on the beat after overcoming alcoholism. She chooses the young lieutenant for her vice squad. The very enthusiastic Antoine learns all the ticks of trade alongside the other officers in Carolines squad. She very quickly gets attached to the young man, who is the same age as her son, if he had been alive.