One night, three young men shoot the owners of a hunting lodge. The man who hired them claims he only asked them to do one thing: scare the people who were resisting him. How do you come to kill when you're barely twenty and there's no war going on?

After completing his military training, young Léo, a taciturn soldier with family problems and secret addictions, is assigned to one of the units that patrol the streets of Paris in search of possible terrorist threats as part of Operation Sentinelle.