An FBI undercover agent, Joe Pistone, infiltrates the Mob in New York under the alias Donnie Brasco. He befriends an aging hitman, Lefty Ruggiero, who takes him under his wing, not knowing Donnie’s true identity. As Donnie delves deeper into the Mafia hierarchy, he gains the trust of several mobsters, including Sonny Black, a powerful and ambitious caporegime. The line between his new identity and real life starts to blur, testing his loyalty and morality. His undercover work starts to take a heavy toll on his personal life, straining relationships with his family who are oblivious to the dangerous role he plays in the criminal underworld.

The deeper Donnie gets, the more he finds himself identifying with the men he is supposed to be deceiving. He witnesses the brutal reality of the Mafia, marked by violence, betrayal, and the strict code of honor that governs the criminal life. The consequences of his actions become more significant, and the risk of exposure grows with each passing day. Entrapped in a world of duplicity, Donnie must navigate a dangerous path that threatens his identity, his family's safety, and the lives of the men he has come to regard as friends. This internal conflict and the moral dilemmas it spawns form the crux of his journey, as he walks the fine line between duty and honor, and the personal cost of living a lie.