Reno Davis is an American writer who has recently retired from boxing. Now unemployed and broke in France, he encounters the wealthy widow of a French general. Anne de Villemont is attracted to Reno, and he to her, but she keeps him at arm’s length. She also hires him to tutor her eight-year-old son Paul. The real reason she wants Reno is for protection.
Reno is led to believe that Anne’s husband was killed in the Algerian conflict, and he is troubled by Anne’s intense fear that Paul will be kidnapped. He then discovers the family has ties to a fascist organization that plans to take over all of Europe. He takes on the shady psychiatrist Morillon and mysterious family friend Leschenhaut, both of whom frighten Anne whenever they are around.
Reno is framed for his best friend’s murder as he and Anne become the targets of the ambitious and maniacal schemers who wish to rule Europe. Reno and Anne are hunted around France while protecting Paul from being abducted. The chase ends at the Colosseum in Rome, where Reno and the villains engage in a showdown.