It sounds like you’re referring to (known in English as The City of Fear ), a cult French comedy film from 1994 directed by Alain Berberian, starring the legendary comedy trio Les Nuls (Alain Chabat, Chantal Lauby, and Dominique Farrugia).
Simon accuses Serge. Serge, flustered, admits he wrote the script. But then Serge accuses Agnès. Agnès accuses the caterer. It’s a mess. Finally, through a series of absurd deductions (including a clue about a rare type of breadcrumb found at every crime scene), Simon realizes the truth. cite de la peur
Simon, despite being a complete failure as a detective, gets the girl. He and Agnès kiss while a subtitle on screen reads: "They lived happily ever after. Until the sequel." It sounds like you’re referring to (known in