The Round House opens in the spring of 1988 on a North Dakota reservation where a woman has just been attacked and raped. As the crime comes under investigation, the victim, Geraldine Coutts, descends into silence, unable to relive her traumatic experience and thereby causing the details of the crime to remain unknown not only to the police, but also to her husband Bazil and her son Joe. For Joe, the attack upsets his whole world. The close-knit family he once knew begins to fall apart as his mother plummets into solitude, unable to leave her room.
Being left to his own devices prompts the thirteen-year-old Joe to grow up quickly. As his father, a tribal judge, attempts to find justice through the system he is supposed to believe in, Joe becomes increasingly frustrated, with the federal investigation and his father's efforts appearing to lead nowhere. Hoping to repair his once happy family, Joe takes matters into his own hands. With the help of his best friends, Cappy, Zack, and Angus, Joe sets out to find answers.
Joe's hunt for justice takes him to the scene of the crime, the round house, and acquaints him with a variety of characters. He meets several dead ends until he learns of Linda Lark. Through old case information of his father's, Joe becomes interested in the Lark family, particularly Linda and her brother Linden. Gaining Linda's trust and friendship, Joe inquires into Linden and his life. It soon becomes apparent by Linden's nature and actions that he attacked Geraldine. Unable to wait for the authorities to come to the same conclusion, Joe becomes the enforcer of justice. He waits for Linden on a golf course, where he shoots him; however, Linden is only wounded by his two unsteady shots. However, Cappy had been hiding in the woods and ultimately delivers the kill shot.
Linden's sudden death arouses the suspicions of Joe's parents, as a number of signs point towards him. However, in the end, the crime remains untied to Joe, even though those closest to him are aware of his actions. The story closes with Joe and his parents driving home from the hospital after a car driven by Cappy overturns, injuring Joe, Zack, and Angus and killing Cappy. While nothing is said between the three people, Erdrich gives the reader the sense that the Coutts family is slightly restored.