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.

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.