Brother Cillian is a Catholic priest at the North Dakota Boarding School for Native Americans. After Teonna Rainwater escaped from the school, he, Liam, and Romero were ordered by Father Renaud to ride out and recapture her. While Liam was attempting to deliver a young boy back to the school, he and Romero discovered Teonna masquerading as a boy. He jumped on her and she gouged one of his eyes. He attempted to kill her only to be shot by Hank Plenty Clouds. He survived the shot to the back while Romero was killed, in which he grabbed Hank's shotgun and killed him with it. While reloading, Teonna picked up a large rock and crushed Cillian's head with it. His corpse is later scalped along with Romero's by Runs His Horse with a blood writing, Child Killer, written on his torso.