Maggie is one of the original explorers on the Sea Foam, a generation ship on a 400-year journey to a potentially habitable planet. To maintain her emotional connection to Earth, she tells her two children, Bobby and Lydia, creation myths from around the world. After a long while without contact, Earth gets in touch and shares a scientific advancement that allows people to become immortal. Maggie and her husband João argue about the ethics of immortality. João feels he will lose his humanity if he becomes immortal, whereas Maggie feels that death is ultimately what robs people of their humanity. Compounding the issue is the fact that the ship can only sustain a set mass of people, meaning that some people must die in order for children to be able to grow up and take adult places in terms of the mass the ship can support. For each adult who decides to live forever, one of the existing children on the ship must decide to remain a child. Ultimately, Maggie decides to remain, and João decides to grow old and die. This means their two children must choose: one will grow up, and the other will remain a child. Bobby chooses to remain a child and is happy with his choice, though as the decades and centuries pass, Maggie finds the ancient adult in a child's body increasingly unsettling to be around. The Sea Foam finally reaches the target planet only to find it already colonised by robots who have been waiting for them. These robots are the next evolution, or wave, of humanity - and with their increased tech, they left Earth long after the Sea Foam but overtook it along the way. They offer the colonists the chance to upgrade into robotic forms and join the world-mind they all share. Bobby accepts first, and the choice puts more distance between he and Maggie. Maggie's granddaughter Sara is also converted, but Maggie holds out as human for a long time before deciding that if she was able to accept immortality and retain her humanity, she can accept this. As part of the shared consciousness, she continues to tell her creation myth stories. They spread out to colonise the universe, and are eventually overtaken by another new 'wave' of humanity - beings of pure energy. Offered a choice yet again, Maggie chooses to become part of the light. After spending aeons traversing the galaxy - and reconnecting with Bobby - Maggie finds herself on a nice rocky planet that reminds her of earth. She sculpts a clay version of her long-dead husband from river mud, evoking memories of the creation myths. Then she finds an interesting animal species, reaches into their heads and tweaks something in their genes that will eventually lead them to evolve into intelligent beings, planting the seed for the next wave of life.