The young Daniel was guillotined for the murder of a policeman. Shortly after, his brother Jean has a terrible accident on a race track and shows irreversible brain damage. A medical team lead by Dr. Duval decide to attempt the first brain transplant on a human on Jean.

Following a long period of rehabilitation, Jean's memories and personality are rebuilt. His physical recovery is complete, but exhibits some strange behavior...

After the murder of Marianne Laforet, Jean attempts to escape by motorcycle, but is apprehended by the police.

Jean's trial starts. Meanwhile, a debate starts on the nature of brain transplant surgery - with the brain of another individual, can one maintain their own personality?