One night in Tampa, Florida, Mickey Duka leads the young Bobby Saint to an arms deal. The deal is brokered by a man named Arnold Creed, who speaks with an accent due to his knowledge of six languages. The exchange goes bad when FBI suddenly burst into the scene, and agitated, Arnold pulls out a gun. The police fire back, killing everyone except the cowardly Mickey, who is terrified when he sees Bobby's body.
The bodies are taken away, but Arnold Creed stands up unharmed, and speaks with an unaccented voice that he hates the undercover jobs he's always been taking. Arnold Creed is really Frank Castle, a FBI agent who is just retiring. This case had been his last, and he was upset at the death of the young man. The police are ill at ease when they discover who the young man is, Robert Saint, son of crime lord Howard Saint. When the news reach the Saint family, the second son Johnny orders Mickey to be bailed out. Mickey is taken by the Saints to a club and beaten. He explains to Quentin Glass that Robert "Bobby" Saint came of his free will, and that the Arnold Creed, the man responsible for the deal, is dead. Howard is still unsatisfied, and kills another man who was supposed to be responsible for his son in front of Mickey.
Meanwhile, Frank returns to his family, his lovely wife Maria and young son. Frank knows he has been neglecting them and forcing them to move constantly, but he promises London would be the last place to move to. Before that though, they will go to a family reunion in Puerto Rico.
Howard Saint goes to confirm his son's body, and when the police proved unwilling to share information with him, he orders his own men to find out everything about Arnold Creed. At the funeral of his son, Quentin informs Howard that Arnold Creed was a fake, that his real name is Frank Castle. Howard orders him killed, but his wife Livia adds that the whole family must also die. Howard agrees, while Johnny decides to go to Puerto Rico with the other assassins.
The assassins arrive just in time for another family outdoor beach party. Frank has gone inside with his father to look at some modified guns, they hear the gunshots. Though they fire back, they are unable to rescue anyone. The assassins completely slaughter the family, and although Maria and her son manage to escape in an SUV and drive away, the assassins eventually catch up and run them over on a pier. Frank, distracted by a knife fight, arrives too late. The assassins return, and Johnny beats and shoots Frank himself, telling him "My father and mother send their regards". Quentin then torches the place, and they leave Frank for dead, not knowing that the explosion actually blasted Frank into the water. They return to the Saints & Sinners club, where they toast to "a score settled", and Howard gives Livia a pair of diamond earrings to celebrate. Quentin slow dances with Livia as Howard watches, then Livia strips off her dress for Howard when they are alone.