Androids Mother and Father flee an uninhabitable Earth to settle on the planet Kepler-22b and start a family with six human embryos. Twelve years later, only one child, Campion, remains. As Mother and Father begin to malfunction, the arrival of the Ark of Heaven – a spacecraft carrying the Mithraic, a religious order of surviving humans – presents a threat that Mother has no choice but to confront.

After her confrontation with Marcus and the Mithraic, Mother takes five of their Earth-born children – Tempest, Paul, Hunter, Holly, and Vita – to live on the settlement. As she and Father attempt to put the shaken newcomers at ease, Marcus struggles to survive alone on Kepler-22b. Meanwhile, Campion tries to ingratiate his new friends but begins to question Mother’s motives.

When the Mithraic kids fall sick with a mysterious illness, Campion suspects Mother is poisoning them and plans an escape. As Mother and Father attempt to prove their good intentions, Marcus and Sue, desperate to get their son Paul back, work to convince the other surviving Mithraic to mobilize a rescue party for the children.

After reconnecting with her creator, Mother finds herself distracted by intense feelings, leaving the settlement vulnerable to Marcus, Sue and the Mithraic; as Campion questions his family's principles, the other children's loyalties are tested.