Based on actual events, this French thriller follows inspector Roger Borniche (Alain Delon) in his three-year pursuit of serial killer Emile Buisson (Jean-Louis Trintignant), who murdered more than 20 people and committed more than 100 robberies after his escape from a psychiatric hospital in 1947. After spending years on Buisson's trail -- and several more dissecting his crimes -- Borniche leaves him in the capable hands of an executioner.