Ngoc Minh Quan runs a Chinese restaurant in London with his business partner Lam. When his teenage daughter Fan is killed in a clothing store bombing, he seeks revenge. The bombing is claimed by a group calling itself the “Authentic IRA”. Failing to get the names of the bombers from Scotland Yard, Quan next focuses on the Northern Ireland deputy First Minister Liam Hennessy, who speaks publicly about his status as a former IRA leader while condemning the bombing. Quan eventually leaves for Belfast and seeks out Hennessy, who claims to have no knowledge of the bombing or its perpetrators. Quan does not believe him and sets off a homemade bomb in Hennessy’s office as a threat unless he gets the bombers’ names. Hennessy tries to identify the bombers with help from his contacts, but the rogue members catch on and outwit him. Quan observes Hennessy seeing his mistress, Maggie, and photographs them. Quan then brings the fight to Hennessy, hiding in the woods outside his Belfast farmhouse and attacking it with more explosives. As Hennessy’s men attempt to track him in the woods, Quan uses traps to disable them, but is shot in the shoulder and flees. Hennessy sends his nephew Sean, a Royal Irish Regiment soldier, after Quan in hopes that his tracking skills can be used to stop Quan for good. As Quan cauterises the gunshot wound, he has flashbacks of his escape from Vietnam to Singapore by sea, where he and his wife lost their other two daughters to attacking Thai pirates. Hennessy receives files from the British government on Quan’s true background: a Chinese Nùng former Vietnam War special operations forces soldier who was trained by the US Army. After a second bombing on a double-decker bus, Hennessy negotiates with British politician Katherine Davies and promises the capture of the bombers in exchange for the pardoning of several of his former IRA comrades. Meanwhile, Hennessy receives intel on the bombers and relays the information to Sean and police. After a knife fight in the woods, Quan captures Sean, who names the bombers and their location. Quan then lets Sean go. Hennessy interrogates his head enforcer McGrath, discovering that the true mastermind is Mary, Hennessy’s wife, who also hired Maggie, who remains angry at the British for the death of her brother and resents Hennessy’s working for them. Hennessy executes McGrath for his betrayal and for involving his wife and mistress, then rebukes Sean for leaking information to Mary. As police prepare to raid the bombers’ hideout, Quan enters the flat disguised as a handyman and kills everyone but Maggie. Quan leaves just before the police raid the apartment and find a severely wounded Maggie. They torture her into disclosing the location of their next bomb, which has been planted in a laptop computer to be detonated on a plane. British police find and throw the laptop into an empty jet bridge, where it detonates without casualties. With the threat resolved, Maggie is executed to prevent any “loose ends”. Hennessy gets a call from Davies, who tells him that she has learned of his involvement but that he will retain his position as a politician, though under her thumb. Meanwhile, Sean executes Mary; thus the entire cell is eliminated. Quan confronts Hennessy with the picture of Hennessy kissing Maggie, which is enough to throw public suspicion on Hennessy and his role in the bombings. Quan forces him to post the picture to the internet. Meanwhile, Scotland Yard realizes Quan’s role in the events and has him put under surveillance, but decides not to take any further action as thanks for his assistance. Quan returns to his restaurant and Lam hugs and kisses him. Quan finally puts the past behind him and begins to heal.