Set in some small southern California town, The Hillz follows the experiences of a promising athlete named Steve (Jesse Woodrow) and his friends. Steve's three friends, Duff, Seb, and T, all come from wealthy families and spend most of their time getting high, drinking at parties, and harassing Ahkmed, a convenience store clerk. After finding a gun in a girl's house, Duff starts violently pursuing a life of crime with T, the loudmouthed instigator with a Napoleon complex, at his side.
After Duff kills a local kid who volunteers at the police department, the story flashes forward one year later with Steve returning home from college after being successful in college baseball. Steve came back to get his dream girl, Heather Smith (Paris Hilton), who told him that if he made it as a baseball player she would consider dating him. Steve runs into Duff's gang. Things spiral out of control for Steve as we learn that Duff and T have become submerged in what they think is one of the hardest gangs ever. Duffy has recently been drafted into the U.S. Army and fears of being sent to Iraq to fight where he might not return.
Shortly after Steve joins up with Duff and T, he witnesses them kill a man in broad daylight in the middle of the street over $80. As the story unfolds, it is clear that Heather is being used and abused by her new boyfriend Todd, whom she is reluctant to leave for Steve. Later, Steve convinces Seb, who broke his ties with Duff's crew, to come out and party with Duff and the old gang for a night.
Meanwhile, T insults two Korean men by calling them Gooks, who then fire an Uzi into Duff's car, killing Seb. Duff and T are later sold out to a crooked undercover cop and the older brother of the man who was previously shot over $80. They killed T and then a narcotics officer, and his team busted the door down and were all killed.
In the final scene, Steve and Duff are driving along the street when a couple of young kids throw rocks at Duff's car causing the two get to out of the car and chase after them. As they get near the kids, one of them turns, pulls a gun, and shoots Duff and Steve, killing them both.