There's Going to Be a Party(1960)

Ça va être ta fête

FBI agent John Lewis travels in Europe, from Paris to Lisbon, trying to locate a disappeared fellow secret-agent, Mark Lemoine. Soon he has trouble with a violant gang, and is involved with a young French reporter, Michèle Laurent. Finally, the chief of the Secret Service tells Lewis that Lemoine never existed. Instead of ending his mission there, the real trouble starts.