The story details the return of Richard to his home town of Matlock, Derbyshire in the Peak District, England, after serving as a paratrooper in the British Army. Richard and his younger, mentally-impaired brother Anthony, camp at an abandoned farm near the town. Flashbacks reveal Anthony’s abuse by a group of drug dealers in the town; Richard vows to take revenge.
Richard has a face-to-face confrontation with Herbie, one of the abusers, who does not recognise him at first. Later, Herbie and friends Soz and Tuff are in a flat taking drugs. He tells them about the confrontation, and states he thinks the man might be Anthony’s brother, who has been away serving in the army. When Herbie leaves he sees a man in a military gas mask banging on the front door of the block. Soz and Tuff run outside but the man is nowhere to be seen. When they go back into their flat they discover Richard has ransacked it, stolen the drugs and spray painted the words “Cheyne Stoking”, a pun on the scientific name for the pattern of breathing a human being goes into when they are dying.
The next day the thugs visit Sonny, the de facto leader of the gang, to explain where the drugs went. When they meet, Sonny has had his face painted but doesn’t realise. The other gang members arrive during this time and they have had their hair and clothes painted as well. They all suspect one another of playing games until Herbie states that the man he saw in the pool hall is Richard, Anthony’s brother. All of the gang become silent as they realise that Richard is back in town.
The men encounter Richard while driving in their Citroën 2CV. He makes it clear that he is not scared of any of them and invites them to come and find him at the old farm where he is staying. The gang leaves with Sonny visibly concerned at Richard’s apparent lack of fear. That evening, while the gang are hiding out and playing cards, Sonny decides that they should shoot Richard. When one of the members leave, Richard (having sneaked into the house) brutally kills him with an axe, using the dead man’s blood to smear the words “One Down” on the wall.
The next morning, they take their car and go to the farm where Richard is staying with Anthony. Sending in Big Al (one of their members) to draw Richard out, Sonny prepares to shoot him with a rifle and their only round. However, he misses and kills Al. With no rounds remaining in the rifle they retreat and return to town, while Richard smiles.
The surviving members stop at a local petrol station where the car breaks down and Tuff runs off, scared of Richard’s revenge. Later at Sonny’s house, they arm themselves and search the place, expecting Richard to be there. They do not find him, although he is hiding in the kitchen pantry. While they are upstairs Richard laces their kettle with a cocktail of the drugs he took from the gang earlier in the film. The three men become completely intoxicated a few hours later and Richard reappears to kill them one by one. He toys with them, dancing and joking. He shoots Sonny in the head, and kills Soz with an upward palm strike. He then sits down Herbie and brings out a suitcase, which has Tuff’s corpse inside. Richard then tells him he is a good man and will let him live if he tells him where the final gang member is as he left the gang years before. He tells him without hesitation and Richard hugs him. But he finds Herbie’s knife and asks him if it was to be used on him. Herbie lies at first then tells the truth, but Richard stabs him regardless. Richard leaves right after.
The next day, Richard arrives in a nearby town where the final gang member, Mark, lives with his wife and two boys. He talks with the children’s mother and asks her to let her husband know that he is Richard, Anthony’s brother. When Mark returns home, she explains the conversation to her husband. Terrified, he tells her how the gang abused Anthony. The abuse culminated with them pretending to hang him at a local ruined castle whilst he was high on acid. This final episode of abuse culminates with Anthony actually hanging himself after his ‘friends’ run off. It then becomes clear that Richard has been alone the whole time, and talking to a vision of his dead brother.
The next morning, Richard sneaks into Mark’s house and takes him hostage using a knife. He makes him drive to the same ruined building where Anthony hanged himself and demands he tell him his part in what happened. Mark explains how his fault was in not stopping the abuse. Richard confesses to his crimes against the other men, and reveals that he thought of Anthony as an embarrassment to him because of his mental disabilities. He tells Mark how he now feels like the monster and that he simply wants to lie down with his brother. Richard gives the knife to Mark and demands that he kill him lest he continue his monstrous ways. Mark refuses but Richard clasps his hands and pulls them towards him. Mark eventually stabs and kills Richard, then stumbles away.