Plot
The film opens with three men burying an unseen figure, which is on fire, in a secluded field.
Bull is a mysterious man seeking vengeance on the men that tried to kill him. He systematically works his way through the group that double-crossed him, beginning with an unknown man whom he brazenly murders in the street before moving on to his ex-wife's auntie, Cheryl. He kills her and her husband Ollie in their home before finding and killing Marco, one of the gangsters involved.
Through flashbacks to ten years ago, it is revealed that Bull was an enforcer working for his father-in-law Norm, a ruthless gang boss. Bull's unrestrained psychopathy and tremendous capacity for violence was an effective tool for their work, but put everyone on edge. Bull learns that Gemma is cheating on him with his colleague, Gary and also that she is using Heroin. Norm attempts to convince Bull to divorce his cheating wife, and to also let him and Gemma hold custody of his son Aiden, so Gemma can marry her lover and Bull's colleague in the gang, Garry. Norm's reason to arrange a marriage between his daughter and Gary is to take advantage of Gary's connection to the drug trade to make more money than their loan sharking business. After failing to convince Bull since Bull does not want to give up custody of Aiden, Norm, Gemma, Gary, Marco and Clive kidnap him and bundle him into the back of a car, with Clive apologizing to him as he closes the boot. They drive him to an abandoned caravan, burn him alive, and shoot him in front of Aiden. Nobody knows how he's returned, but Norm promises Gemma vengeance for her auntie’s death.
Norm finds Bull's mother Marge and tortures her for information, against the wishes of his gang. It is revealed that Bull has been watching all of this without helping. He enters his mother's home and asks her if she wants "help", then smothers her to end her suffering.
Clive, a gang member who has always been terrified of Bull, is walking his kids home when Bull pulls up and kidnaps them. He takes them to the funfair and threatens Clive into luring Gary to the fair. Once Gary arrives, Bull lets Clive and his children go home. He takes Gary hostage with a knife, interrogates him to find out which town Gemma is now living in, and slashes his thigh while they ride on the waltzers, leaving him to bleed out.
In Gemma's town, he tracks down a heroin dealer and cuts his hand off, takes his money, then forces him to reveal Gemma's address. With the heroin dealer unconscious in the back of the car, he drives to Gemma's house, breaks in, and forces her to trick Norm into coming by. When Norm arrives, he believes the unconscious drug dealer to be Bull, and orders gang member Colin to shoot him dead. However when he enters the house, Bull ambushes him with a knife. He tortures both Norm and Gemma to get his son's location. Gemma reveals that Aiden, after being forced to watch his father burned alive and shot, became a heroin addict as well. He smothers Norm and shoots Gemma dead. He then goes to a notorious part of the town and finally finds Aiden, high on heroin, asleep under a bridge.
He carries his son to a church where they spend the night. The next morning the vicar finds Aiden asleep under the altar. She rushes to his aid but is suddenly sent into a fit of terror when she sees Bull. She demands to know how he dares enter a house of God. When he turns, his eyes are pure black. Through brief flashbacks, it is revealed that his eyes have in fact been pure black throughout the story. He begs the vicar for his son's salvation, and leaves Aiden and the vicar with the money he took from the heroin dealer.
Bull later returns to the field in which he was buried at the start of the film. It is then revealed that he truly did die that night, and it's strongly implied that he made a deal with the devil to return and avenge his own death.
