Payback

In a filthy kitchen of an underground abortionist, an unkempt former medical doctor puts on surgical gloves and quickly downs a full glass of cheap whiskey. Face down on the kitchen table is a barely conscious Porter (Mel Gibson), severely wounded with two large bullet wounds in his back. The doctor pours whiskey on Porter's back to sterilize the area and digs out the bullets. Porter spends five months recuperating. Porter narrates that he had $70,000 taken from him and that is what he was going to get back.
Porter begins tracking down gangster Val Resnick (Gregg Henry), his violent former partner, and Lynn (Deborah Unger), his estranged wife and a heroin addict, both of whom betrayed Porter following a $140,000 heist from the local Chinese triads. After Lynn shot Porter and the two left him for dead, Val rejoined the Outfit, a powerful criminal organization, using $130,000 of the heist money to repay an outstanding debt. Porter is intent on reclaiming his $70,000 cut.
Porter first tracks down and confronts his wife Lynn, who has at this point become a prostitute out of shame of shooting him. After seeing how low she has sunk into drugs and prostitution, Porter takes pity on Lynn and confines her to her bedroom, only to discover the next day that she has died from a heroin overdose. (Whether Lynn's overdose was a suicide or an accident is never made clear).
Porter enlists the help of a call girl, named Rosie (Maria Bello), who is affiliated with the Outfit. Porter once served as her limo driver, during which time they had a one-night stand. Lynn's jealousy and the fact that Porter had cheated on her with Rosie led to her and Resnick double-crossing Porter. To get to Resnick, Porter must deal with a lowlife drug dealer and gambler named Arthur Stegman (David Paymer), crime bosses from the Outfit, the Chinese triads, and two corrupt police detectives named Hicks and Leary (Bill Duke and Jack Conley).
The sadistic Resnick is seeing a dominatrix named Pearl (Lucy Liu), who has connections of the Chinese triads, when Porter violently re-enters his life. Resnick goes to the Outfit to explain why Porter is demanding $70,000. Told to handle it himself, Resnick tries to, but is shot and killed by Porter in Rosie's apartment as Porter catches him abusing Rosie when Porter returns to collect his forgotten cigarettes.
Porter then kills three of the Outfit's hit squad henchmen, including their leader, Philip (John Glover), who have been sent by Carter (William Devane), their immediate superior with the Outfit, to "Stitch this mutt up."
That evening, Porter confronts Carter in his office and threatens to kill him if he refuses to pay his $70,000 as compensation for the late Resnick's betrayal. Carter explains to Porter that he is only an underboss and is not authorized to make any financial decisions. Porter then forces Carter to phone the top mob boss in the organization to take the issue with the top man. (Note: each villain says that Porter wants $130,000 from Resnick's paid debit, but Porter keeps correcting them and saying "It's $70,000!"). Porter hears the refusal of the top mob boss Bronson (Kris Kristofferson) on the phone, so he carries out his threat and shoots Carter dead.
With the aid of Rosie, he kidnaps Bronson's son Johnny, keeping him tied up. He arranges for Hicks and Leary to be busted by their own colleagues in Internal Affairs by planting Leary's fingerprints on the gun Porter used to kill Resnick. He pick-pockets Hicks's badge, then leaves it with the gun in the hand of Resnick's dead body.
The next day, Bronson and his mob associate Fairfax (James Coburn) join the hunt to take him down. Porter is captured by the Outfit's men after a wild chain of events and a shootout involving Stegman, as well as Pearl and triads, which ends with Stegman and all of Pearl's henchmen being killed (only Pearl survives). Porter is taken to a warehouse where he is beaten and tortured for several hours by the Outfit's men, leading to having two of his toes smashed with a hammer to force him to give up the location of Bronson's son.
Porter is locked inside a car trunk and taken by Bronson and his men to an apartment that had previously been rigged by the Outfit's man, Philip, to a phone connected to plastic explosive. After his captors meet an explosive demise, Porter is picked up by Rosie (with her dog, also named Porter). When she sees his injuries and asks what happened, Porter replies, "I got hammered." Taking the $130,000 the mob owed him, they drive off to Canada to begin a new life.
Director's Cut[edit]
The Director's Cut (dubbed Payback: Straight Up) has a largely similar foundation but explores the betrayal of Porter through flashbacks and most significantly removes the Bronson character from the screen. Instead a female voice (belonging to Sally Kellerman) on the telephone replaces Kris Kristofferson. The scene with the booby-trapped telephone is eliminated, as is the kidnapping of Bronson's son. In this version, Val kills Rosie's dog Porter.
The simplified story line ends with Porter collecting his money at an arranged drop in a train station where he has several shootouts with syndicate hit-men staking out the station. He is seriously wounded and seemingly near death before being driven away by Rosie with the money. The Director's Cut also lacks the theatrical version's voice-over narration by Porter.

Question: Who kills Rosie's dog Porter?
Answer: Val.; Val.