Gérard tells the story of a brother and sister, Paul and Lise, who live in a fantasy world of their own imaginings. They are severed from the outside world when Paul – after being struck by a snowball thrown by his idol Dargelos – falls ill and is forced to stay home from school. Shortly thereafter, their mother’s untimely death leaves them completely alone.
Isolated and totally dependent on each other, they pass their days in their “Room”, acting out their wild fantasies, which they term “playing the Game”. At first innocent, these games become increasingly twisted. Gérard, their only friend, visits them and serves as their private audience.
Lise, growing tired of this oppressive situation, eventually gets a job as a model. She befriends another model, Agathe, and brings her home. Agathe looks exactly like Dargelos, and her presence further threatens the delicate balance that these “children” have created.
Lise’s last chance to get away crumbles when her finance Michael dies in a car crash. Fate has set the stage for tragedy. Unable to accept that her brother Paul has fallen in love with Agathe, Lise acts to prevent it. She tricks their friend Gérard to marry Agathe, insuring that she and Paul will never be separated. But the “magical” world the two of them had before cannot be recreated. Paul tries to poison himself, and in the confusion that follows, the truth about Lise’s plot comes out. What had begun as an innocent children’s Game ends tragically in death and destruction.