In 18th-century France, naturalist GrΓ©goire de Fronsac and his Iroquois companion Mani arrive in GΓ©vaudan to investigate a series of brutal killings blamed on a mysterious beast. They uncover a conspiracy as local nobles and the church use the beast to instill fear and maintain power.
As Fronsac investigates, he develops a romance with Marianne, the daughter of a nobleman, while also encountering Sylvia, a courtesan with hidden motives. Meanwhile, Mani, skilled in combat, discovers the beast is not a supernatural creature but a trained animal used for terror.
Mani is killed while trying to expose the truth, pushing Fronsac into action. He uncovers a secret cult, the Brotherhood of the Wolf, responsible for the killings to oppose the monarchy. Seeking revenge, Fronsac, now a fierce warrior, destroys the cult members.
In the end, Fronsac kills the beast and exposes the conspiracy, but he loses both Mani and Marianne. Disillusioned, he leaves France. The film ends with the ominous reminder that power and manipulation remain ever-present in society.