The story revolves around the character of Richard (Paddy Considine), a paratrooper returning to his small home town of Matlock in the Peak District. Richard has returned home from the army to exact revenge on the tormentors of his mentally disabled younger brother Anthony. In the opening line of the film, Richard narrates "God will forgive them. He'll forgive them and allow them into Heaven. I can't live with that." Richard and Anthony camp at an abandoned farm near the town, their reminiscences of childhood interspersed with flashbacks to Anthony's ordeal at the hands of the gang youth, and Richard's subsequent revenge. This revenge starts when the gang and their leader Sonny find out about his presence. He confronts Richard in a failed attempt to intimidate him. Richard's revenge begins with the older members of the gang. While they are asleep he sneaks into their house, wearing a green boiler suit and a gas mask. He spray paints one of the two men's hair multi-coloured and paints a target on the back of the other's suit. On the same evening he enters Sonny's house and applies make up to Sonny's face.However things soon turn nasty as Richard sneaks into a club where the gang are hiding out and playing cards and kills one of their members with an axe, using his blood to scribble the words "One Down" on the wall. The gang 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. However, he misses and kills Al. With no bullets remaining in the gun he decides to quickly retreat and return back to town.The surviving members return to a local petrol station where Tuff runs off, scared of Richard's revenge. The other three return home, they search the house expecting Richard to be there. However while they are upstairs Richard laces their kettle with a sizeable amount of drugs (LSD/Ketamine) taken from the gang earlier in the film. The three men become too intoxicated to properly react to Richard's presence and he kills them one by one. He shoots Sonny in the head, palm-strikes Soz at such an angle that he is killed, and finally stabs Herbie. Before killing Herbie he reveals he has already killed Tuff, although it is not revealed how, by producing his corpse in a suitcase.With one member of the original gang left - a reformed character with a wife and children - Richard abducts him and takes him to an old outbuilding. It is now revealed that Anthony died long ago, hanging himself after the gang abandoned him with a noose around his neck. The Anthony that is seen with Richard throughout the film is, in fact, a hallucination. During this confrontation, Richard confesses to his heinous crimes, describing the blood on his hands, saying " Now I'm the monster...", and "You were supposed to be the monster...now I'm the fucking beast." He describes the crimes he's committed and is unsure of what else he's capable of doing, he also says that all he wants is to lie down with his brother, and demands the final gang member kill him, which he does, after Richard tells him to think of his children and begging him to kill him. The gang member is then shown distraught, with his hands covered in blood. He then leaves and the camera then pans across the landscape.
Output: Question: Who is the leader of the gang ?, Answer: Sonny