An unnamed hobo David Brunt arrives by boxcar in the city of Hope Town, where a graffiti-scarred welcome sign reads "Scum Town." The city is ruled by a ruthless crime lord called The Drake and his sadistic sons, Ivan and Slick. The Hobo roams the suburbs and watches an amateur filmmaker shooting a Bumfights-style movie with homeless people. Suddenly, a bloodied man named Logan, The Drake's younger brother, runs through the streets and screams for help. The Drake and his sons arrive and brand him a traitor to the townspeople before publicly decapitating him with a barbed-wire noose attached to a moving car.
Wishing to buy a lawnmower in a pawn shop, the Hobo begs for change on a sidewalk. However, after seeing a group of punks drag in a homeless man, he sneaks into The Drake's nightclub. Inside, the brothers and their henchmen torture and kill homeless people in arcade-style games. Slick begins harassing a boy named Otis, who owes him money, and Ivan snaps Otis's arm. A prostitute named Abby Cadence MacMichael defends Otis. Slick prepares to kill her, but the Hobo knocks him unconscious and carries him to the police station. There, he learns of the police chief's corruption and complicity in criminal activities. The brothers and the chief carve "scum" into his chest and throw him into a garbage bin. There, he meets Abby, who helps him recover.
The next day, the Hobo goes to the filmmaker and completes a series of degrading acts, including chewing glass, to get enough money to buy the lawn mower. After getting his money and entering the pawn shop, a trio of robbers hold a woman and her baby hostage. The Hobo grabs a shotgun from the shelf and kills the robbers. Realizing that Hope Town needs justice, he buys the shotgun and proceeds to kill dozens of criminals, including the filmmaker, a pimp, a coke lord, and a pedophile dressed as Santa Claus. The Drake, infuriated, lets his sons loose. They enter a school bus and kill the fourteen children inside (who were friendly to hobos) with a flamethrower and burst into a television station to kill the anchorman during a live broadcast for expressing his appreciation of the hobo. They demand that all homeless people be killed or otherwise they would continue on with their rampage, and a mass purging of the town's homeless is launched. The Drake then joins them and orders the Hobo to be brought before him.
As Abby is walking home, a cop Rob Cotterill attempts to rape her. The Hobo kills him and Abby smuggles the Hobo past a group in a shopping cart covered with the cop's remains. Otis spots them, and informs Slick and Ivan. Back at her apartment, the Hobo tells Abby of his plan to leave the town and start a lawnmowing business, which she enthusiastically supports. Ivan and Slick enter and attack the two, wounding Abby. The Hobo overpowers Slick, holds him at gunpoint, and forces Ivan to retreat. The Hobo then shoots Slick in the groin and takes Abby to the hospital. Slick manages to call the Drake before he is taken to hell in a burning school bus. The Drake, mourning the death of his favorite son, summons "The Plague," a duo of armor-clad demons named Rip and Grinder. While Abby is recovering, the Hobo visits the maternity ward and delivers a monologue to the babies. The Plague slaughters the staff at the hospital while looking for the Hobo. When the latter returns to Abby's room, the Plague captures and delivers him to The Drake, who plans to execute him publicly.
Recovered, Abby returns to the pawn shop for weapons. Attaching an axe to the Hobo's shotgun and retrofitting the lawnmower into a shield, she arms a crowd to free the Hobo and bring down the Drake. She confronts the Drake, holding Ivan hostage; the Drake shoots and denounces him a disappointment, much to Ivan's dismay. In the ensuing fight, Abby kills Grinder. Although the Drake severs Abby's hand with the lawnmower shield, she stabs him repeatedly with her exposed arm bone and incapacitates him. Rip tries to persuade Abby to be his partner, but the Hobo drives him off.
The townspeople, motivated by Abby's bravery, show up with their own weapons and aim them at the shocked police, who demand that they leave the area. Seeing that the police will kill the people they failed to protect against the criminals, the Hobo tells the Drake that on their upcoming ride to Hell "You're riding shotgun," and blows his head off. The police shoot the Hobo, and the people avenge him and turn their guns on the police. Both groups exchange fire, while the Hobo dies and Abby's screams are heard.
