Nguyen Ngoc Minh is a Vietnamese restaurateur based in London. He is also a Vietnam War veteran who was trained as an assassin by both the Viet Cong and the US Army. One day, his wife and daughter are killed in a bombing by the Irish Republican Army (IRA).
Nguyen seeks justice, first by going to London Chief Inspector Richard Bromley, who is investigating the bombings, but he rebuffs Nguyen. In the meantime, a rogue cell of IRA continues to commit bombings throughout London. Ian "Woody" Wood, a freelance journalist, is assigned to investigate the IRA. He is approached by the desperate Nguyen, who offers him money for the names of the bombers. Lacking any information, Woody suggests that Nguyen talk to Sinn Féin member and former IRA operator Liam Hennessey. Nguyen sells his restaurant to his best friend and decides to travel to Belfast to talk to Hennessey.
Hennessey has his former weapon dumps investigated, believing a rogue cell is using Semtex from those dumps to create the explosives, but when confronted by Nguyen, he claims ignorance of the bombers' identities. Nguyen reacts to this by setting off a homemade bomb in the bathroom of Hennessey's office. By phone, Nguyen threatens further reprisals if he is not given the names of the bombers.
Hennessey, secretly having ordered the bombings to boost his political needs, is in fact enraged that civilians were killed and that the bombings came without warnings. He summons Sean Morrison, his associate in the United States, to travel to London to talk to Bromley about a plan to take down the bombers. Morrison tells Bromley about their plan, of which only the two of them will have knowledge.
Nguyen sets off bombs on Hennessey's farm, prompting him to send his wife Mary (who is secretly having an affair with Sean) to London. Hennessey sends men after Nguyen, who is positioned in the forest surrounding the farm. As Nguyen is lethally skilled in jungle warfare, he disables Hennessey's men with traps and fights them before escaping into the forest.
When another bombing occurs, Hennessey's plan fails to identify the bombers. Elsewhere, Woody is writing about his meeting with Nguyen. Maggie, a member of the rogue cell, seduces Woody in order to plant a bomb on his laptop without his knowledge before he flies to a press conference.
Desperate to neutralize Nguyen, Hennessey hires a tracker named Kerry, who is the daughter of his close friend and former IRA associate Micky Geraghty. Hennessey discovers that the mastermind behind the bombings is his political enforcer Hugh McGrath. He also discovers Sean and Mary's affair, deducing that Mary and McGrath were responsible for the rogue cell, but decides to let Morrison off the hook to help in hunting down Nguyen.