Anne de Boissy and Lore Fournier are two adolescent Angevin girls who stay at a Catholic boarding school. Both have affluent and conservative families living in the countryside. Anne and Lore quickly become friends. They spend most of their time reading poems about the beauty of death, mocking their classmates and teachers, and engaging in vicious pranks and petty theft, believing that not only is church downright fatuous, but also for idiots, as well as that the both of them together are special, and untouchable. Which is a fact that seems more and more true to them with each passing day when they always manage to escape detection and punishment by usually blaming it on their fellow peers. When Anne's parents take a long trip and leave Anne behind during summer vacation, Lore secretly moves into their château with Anne, where they become lovers and their insidious pranks escalate. The girls set fire to the home of the local cowherd, Émile, and let his cows loose as punishment for his sexual leering over schoolgirls. They also kill all the pet birds of their school's mentally handicapped groundskeeper, Léon, as well as ripping up his clothes and burning some of his personal belongings just to make him suffer. Then afterwards, laugh at his expense. Stealing sacramental bread same with traditional priest uniforms from the church, the girls prepare the abandoned chapel at the château for a Black Mass in which they wed themselves to Satan, promising more wicked works in his name. Even cutting both of their fingers and joining each other's blood so that their bond will become stronger. One night, a motorist runs out of gasoline near the château. The girls invite him in, offer him alcohol, and begin to behave seductively toward him. At first he is confused, then he grows more drunk, as well as eager. Lore continues the seduction, only to become terrified when she gets more than she initially bargained for. The motorist attempts to forcefully rape her out of nowhere as soon as Anne leaves the room by jumping on top of her and trying to suck on her bare breasts after roughly ripping off her bra. Anne shortly thereafter walks in on the scene after hearing her friend's desperate cries of help as she has an intense struggle with the motorist. The man is now trying to pull off Lore's underwear and continuing to vigorously have his way with her despite her repeated pleas for him to stop. At first Anne tries to get him off of Lore, but after being unable to do so and repeatedly pushed away by the stranger, she bludgeons the man to death by picking up a nearby hard plank of wood then hitting him over the head with it. Afterwards the two girls try to conceal the body by wrapping it up in a carpet and dumping it in a nearby lake as they are not sure what to do. Not to mention are horribly afraid of getting blamed for his murder and arrested. Police later find the motorist's abandoned car and suspect foul play. A detective arrives at the château to inquire if the motorist stopped there, but is suspicious when the girls behave nervously and refuse to tell them where their parents are. The girls in turn become convinced that the detective knows what they have done and plan a suicide pact, convinced they will go to Hell and be rewarded by Satan for their service. At a school recital, the girls read out loud a rather grim yet equally eloquent poem by Baudelaire. The nuns become increasingly suspicious as to what Anne and Lore are up to, since they have no idea what the girls are plotting, or of their secret suicide pact. However they are too late to interfere in what is unfolding, and everyone in the room is engrossed with the girls' performance. After reading the poem, while members in the audience start to both cheer and clap in applause, both girls dump petrol on themselves then immediately light a match, lighting themselves on fire as the audience watches totally bewildered. The entire crowd then begins to scream in horror and panic as people realize that the abrupt, shocking finale was in fact, authentic and actually not part of the play at all. Pandemonium breaks out, and fueled by adrenaline, people then proceed to subsequently run towards the exit, in addition to even go as far as to trample at least a couple unfortunate patrons in the audience in an attempt to try to save themselves while evacuating. The two girls' grief-stricken parents watch helplessly with tears in their eyes while distraughtly yelling their daughters' names. With one final look at what has just happened, they have no choice but to join the others as smoke starts to fill up the room. The film cuts to credits as the inferno begins to spread to the front of the auditorium, in addition to the top of the stage which catches the ceiling rafters aflame as the sound of the attendees frightful shrieking can still be heard in the background.
