Bobby Saint, son to Tampa crime lord Howard Saint (John Travolta), accompanies Mickey Duka (Eddie Jemison) to an arms deal with Otto Krieg at the Tampa Seaport. The FBI raid the deal, and when Otto pulls out a gun a firefight ensues between him, the FBI and the Saints representatives. Bobby is killed in the crossfire, and Mickey is arrested. Otto supposedly dies in the firefight, but is actually revealed to be undercover FBI agent Frank Castle (Thomas Jane), the operation being his final before his retirement.
Meanwhile, Bobby’s death enrages Howard, added to the fact that his son only came along to the deal in order to impress his father. His right hand man Quentin Glass (Will Patton) bribes the FBI into obtaining information on Otto, revealing his true identity to Howard. Quentin is ordered to kill Frank, on vacation in Aguadilla Bay, Puerto Rico with his entire family. Howard’s wife Livia demands Quentin kill the entire family in revenge.
At the reunion, Quentin and John Saint along with several other of Howard’s man massacre the entire Castle family. Frank and his father manage to kill several gunmen, however Frank’s dad is killed by one who stabs him in the back. Castle’s wife and son are both ran over and killed by John, who then proceeds to execute Frank before exploding him off a pier. Frank’s body washes ashore near the hut of a local witchdoctor, who nurses Frank back to health. In returning to the location of the massacre, Frank finds the iconic Skull print T-Shirt that his late son bought him as a retirement gift.
Frank returns to Tampa and takes up residence in an old tenement building, along with Dave, Bumpo and Joan. Castle abducts Duka, who willingly becomes Castle’s mole within the Saints family. Frank uses the information Duka passes onto him to sabotage Howard Saint’s money laundering and drug import operations. In a following scene, an abusive ex boyfriend of Joan’s threatens her outside of her apartment. Frank intervenes when he turns his attention on Dave, the first time anyone has ever stood up for him. Frank’s neighbours, in particular Bumpo and Dave soon learn of the massacre, as well as Frank’s military and law enforcement history.
Frank soon starts to extort money from Quentin in exchange for the many photographs he has of him with his male partner – emphasising that he would not want Howard to learn of this. Frank times this alongside Livia’s routine schedule of going to the movies every Thursday night, laying the ground work to imply that Livia and Quentin are having an affair.