The far-right Organisation armée secrète ("Secret Army Organisation") plots to assassinate President de Gaulle. The first attempt on 22 August fails, leaving de Gaulle and his entourage unharmed. Within six months, OAS leader Jean Bastien-Thiry and several members are captured, and Bastien-Thiry is executed. The remaining OAS leaders, hiding in Austria, hatch a new plan. They enlist the services of an apolitical British assassin given the code name "The Jackal," a figure already credited with the assassinations of Patrice Lumumba and Rafael Trujillo. The Jackal is aware targeting de Gaulle is extremely risky, but desires a comfortable retirement in anonymity. He insists on a fee of $500,000, half to be paid upfront into his Swiss bank account. The OAS uses its extensive network to raise the money through a series of bank robberies.
Preparing for his mission, the Jackal travels to Genoa where he commissions a custom single-shot rifle from a skilled gunsmith and secures fake identity papers, later killing the forger when he attempts to extort him. In Paris, the Jackal duplicates a key to a flat overlooking a square, setting the stage for the planned assassination. The OAS leadership has meanwhile relocated to Rome, still under the scrutiny of French security forces. French intelligence kidnap the OAS's chief clerk, Viktor Wolenski, who dies during interrogation but not before revealing crucial details of the plot, including the code word "Jackal". The Interior Minister convenes with top security officials and Police Commissioner Berthier recommends his deputy, Claude Lebel, lead the investigation under the constraints of secrecy. Lebel is granted special emergency powers despite de Gaulle's insistence on maintaining his public schedule.
Colonel St Clair, who is de Gaulle's personal military aide and a cabinet member, divulges classified details to his new mistress, Denise, an OAS agent. At the same time, Lebel is informed by Special Branch that a British national, Charles Harold Calthrop, might be connected to the assassination plot and travelling under an alias. The Jackal learns his plot is compromised, but decides to press forward with the mission. He seduces the aristocratic Colette de Montpellier in a hotel in Nice, but narrowly evades capture by Lebel and his team. He survives a motor vehicle collision and flees to Madame de Montpellier's country estate, and kills her when she reveals the police have already questioned her. Dyeing his hair and donning spectacles, he assumes another identity, that of a Danish schoolteacher, Per Lundquist, and boards a train for Paris.
Madame de Montpellier's murder allows Lebel to drop secrecy constraints and launch a public manhunt. temporarily hides at the flat of a man he picks up in a Turkish bath, killing him when the man learns of Montpellier's murder. At a subsequent cabinet meeting, Lebel predicts the Jackal will try to shoot de Gaulle during the upcoming Liberation Day ceremony marking Paris's liberation during World War II. Lebel is dismissed from the investigation so the Minister can assumes personal command, and is then reinstated less than a day later when the Minister recognizes Lebel's expertise.