After Earth is rendered uninhabitable, Androids Mother and Father start a new settlement and family with human embryos on the planet Kepler-22b. Twelve years later, only one child, Campion, remains, and the arrival of an Ark of surviving humans called the Mithraic presents a threat that Mother has no choice but to confront.

After a confrontation with Marcus, Mother discovers and takes five Mithraic children (Hunter, Tempest, Paul, Holly and Vita) back to her settlement. While Mother, Father and Campion, adjust to living with a new group of Earth-born children, Marcus struggles to survive alone on Kepler-22b.

After the Mithraic kids fall sick, Campion believes Mother is poisoning them and plans an escape. As Mother and Father attempt to prove otherwise, Marcus and Sue work to convince the other surviving Mithraic to mount a rescue of the children, desperate to get their son Paul back.

Father tries to teach the children how to hunt some of Kepler-22b’s mysterious creatures for food. Meanwhile, the Mithraic make a stunning discovery that potentially fulfills a Mithraic prophecy, and a debate about how to proceed ignites a conflict between Marcus and the Mithraic leader, Ambrose.

Marcus moves forward with a plan to rescue the Mithraic children, but first he has to find them. Back at the settlement, Campion and Paul bond while on a hunting expedition with Father, and Mother attempts to learn more about her origins.

After rekindling her connection to her creator, Mother finds herself distracted by intense feelings she didn’t know she was capable of having, unaware that Marcus, Sue and the Mithraic are closing in on the settlement.

Marcus’s decisions stress his relationship to his family as he struggles to maintain his clout as leader of the Mithraic. Mother is able to see Marcus for who he truly is, which threatens his power and puts Mother in a precarious situation she might not recover from. Meanwhile, Campion is faced with a choice that could result in dire consequences.