The Conversation (1974)

Harry Caul, a devout Catholic and jazz-loving surveillance expert in San Francisco, is known for his exceptional skills and intense privacy. Tasked with recording a couple's conversation for a mysterious client, he becomes alarmed by what he hears, fearing the couple's lives are in danger. Haunted by a past job that led to deaths, Harry must decide whether to hand over the recording or intervene, thrusting him into a nightmare scenario.