Frain as Richard Shepherd: An assassin who takes a bribe to shepherd Marcus Fox instead of killing him. Guilt-ridden over his actions, he attempts to kill Madison, and covers his tracks throughout the season. Millie Bobby Brown as Madison O'Donnell: A 9-year-old girl who serves as the vessel for Marcus Fox. However, Madison constantly fights to regain her body. When she suffers a bullet wound, Marcus tries to expel her but is himself forced out. She later suffers the consequences of Marcus's actions in her body. Alex Diakun as Marcus Fox: A Qui Reverti member who is a serial killer. When the organization decides to give him a final death, he bribes Richard for one more life. Marcus tries to regain his former status but is unable to dominate Madison's soul, leading to an internal struggle. Episodes References External links Intruders at The Futon Critic Intruders at Rotten Tomatoes 2014 American television series debuts 2014 American television series endings 2010s American drama television series BBC America original programming English-language television shows Television shows based on British novels British fantasy television series