On a cold night in 1978, as Stevo tells Bernie that he was beaten up the day before by the cousin of a woman he assaulted, the group is driving to meet IRA members Chris and Frank. The crew gathers outside a Boston warehouse with intermediary Justine, and a representative, Ord, leads them inside. The group is there to buy guns from arms dealer Vernon and his associates, Martin, Harry, and Gordon. Despite tensions between the two groups and Vernon supplying the wrong rifles, the weapons are unloaded from a van and Chris' group hands over the money in a briefcase.
Stevo realizes that Harry was the one who beat him up the day before, and refuses to go near him, irritating Frank. Harry eventually notices and lashes out at Stevo, furthering the tensions between the groups. Stevo seemingly apologises, but then brags about what he did to Harry's cousin. Infuriated, Harry shoots Stevo in the shoulder. Both groups split off and begin shooting at each other. Martin, who was holding the briefcase, is grazed by a bullet in the head and collapses. The briefcase now lies in the open, with Vernon attempting to coerce his men to get it.
Bernie is shot in the back by Vernon as he attempts to leave and dies shortly after. Soon, two hit-men with rifles begin shooting at both groups. One of them, Jimmy, is killed, and the other is recognised by Ord as Howie, who explains that he was hired to kill everyone and take the money. Before Howie can reveal who hired him, he is shot dead by Chris's group. Chris, defending Justine, requests that Vernon's group let her go. Gordon crawls after her, intent on killing her.
As the shooting continues, a telephone rings in one of the offices. Realising that they can call for backup, Chris sends the wounded Frank to the office, pursued by a wounded Vernon. Gordon chases Justine to the warehouse entrance, but she manages to kill him. As Chris, Ord, Stevo and Harry engage in another shootout, Vernon is severely burned by a fire set by Frank but manages to kill him as he reaches the phone.
Martin suddenly regains consciousness and begins deliriously shooting at his own group. He reveals that he planned to double-cross Vernon and hired Howie and Jimmy to kill the others. Martin gets the briefcase, but soon dies from his injuries. After getting past Ord and Harry, Chris reaches the office and kills Vernon. Using the phone to call his associates, Chris is cut off by Ord while Harry distracts Stevo. Returning to the warehouse, Justine takes Jimmy's rifle but passes out.
Leary, an associate, arrives at the warehouse in search of his IRA comrades, but is beaten to death by Harry. Taking the briefcase, Harry attempts to escape in the van while being fired at by Stevo and Ord. Harry runs over Stevo's head, killing him, but not before Stevo shoots Harry through the bottom of the van, killing him as well. The fire Frank caused spreads and the sprinklers come on. Exhausted and out of bullets, Ord and Chris agree to stop fighting, take the money, and attempt to escape before the inevitable arrival of the police.
Justine shoots Ord in the head and, unintentionally, Chris in the stomach. As Chris lies on the ground, succumbing to his wounds, Justine tells him she regrets that he got in the way. They exchange some last banter, and Justine limps towards the exit with the money, but the sound of sirens grows louder. When red and blue flashing lights appear under the bottom of the exit, Justine realizes that although she survived, she will not escape.
