Jack Whelan is a former Los Angeles Police Departmentdetective who is asked to investigate strange occurrences related to a string of attempted suicides. Despite his efforts, he is stumped. He concentrates his search on a secret society, Qui Reverti, whose members chase immortality by seeking refuge in the bodies of others after their own deaths. Agents of the society, called "Shepherds", find the hosts of the returning souls and show them "triggers"––items important to the returning Qui Reverti members in their past lives––that "awaken" the returning soul. Once awakened, the intruding soul engages in a battle of wills with the host's soul, with the losing soul sent to the afterlife. In Whelan's case, this process destroys his marriage when his wife's body is taken by an intruder. A serial killer named Marcus Fox comes back to life in the body of a little girl. Both souls fight for control, causing their memories to become confused. The struggle is exacerbated when the little girl becomes aware of the Qui Reverti guidebook for returning souls and begins using the information without truly understanding it.
Main cast
John Simm as Jack Whelan:
A former LAPD detective who becomes involved with the Qui Reverti conspiracy. When his wife's soul is lost to an intruder, he destroys many triggers to stop other intruders. Despite this, he is recruited as a Shepherd and instructed to kill anyone who might reveal the organization's existence.
Mira Sorvino as Amy Whelan/Rose Gilcrest:
Jack's wife whose soul is supplanted by that of Rose Gilcrest. It is unknown if Amy's soul is completely gone, given that Rose protects Jack.
Tory Kittles as Gary Fischer:
Jack's friend who was exposed to a machine which allows him to recognize the soul in a body. He sees the soul of friend, displaced by an intruder, in his infant daughter, and becomes increasingly unstable. He commits suicide by jumping off the roof of the Qui Reverti headquarters with information about the organization.
James 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.
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.
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.
