At the height of the Belle ÔEpoque, a mysterious widow comes to the law office of Dubon, insisting that only he can save her innocent friend, an Army captain named Dreyfus who was convicted of spying and exiled to Devil's Island two years earlier. Not wishing to disappoint the alluring widow, Dubon makes some perfunctory inquiries, but when he discovers the existence of a secret military file withheld from the defense during the trial, he embarks on an obsessive pursuit of justice that upends his complacent life.