Ender's wife has joined a religious order, the Children of the Mind of Christ (Filhos de Mente de Christo), and Ender insists on joining with her. His own aiúa now controls his own body as well as young Valentine's and Peter's, but his own body suffers as most of his attention is devoted to the efforts of Peter and Valentine, diverting much of the aiúa of his own body into his other two. Peter (joined by Wang-mu, an intelligent servant girl from Path, introduced in the third book) goes off to distant worlds attempting to manipulate the political arena to ultimately sway enough members of Starways Congress to vote against the destruction of Lusitania. Meanwhile, Miro and young Valentine are spending all available time looking for additional habitable planets. Eventually it is revealed that they are in fact searching for the home planet of the aliens who created the devastating descolada virus, and settling planets was a secondary purpose. This planet is discovered and Miro dubs the inhabitants descoladores. However, the Lusitania Fleet is expected to arrive and destroy Lusitania within a few weeks. Jane is constantly shuttling shiploads of colonists off Lusitania and to the new colony planets in an effort to get as many humans off the planet as possible before it is destroyed.
Peter and Wang-Mu travel to the worlds of Divine Wind and Pacifica to convince the Japanese-led swing group of the Starways Congress to revoke their order to destroy Lusitania. By tracing the decision making trail backwards (strangely going down in ranks, a concept which is explained in the afterwords)they are able to convince a philosopher of his influence in congress. Although with some complication the phisopher gets congress to stop the Lustitania fleet, which was already nearly a swing vote. Regardless,the admiral at the head of the Lusitania fleet disobeys their order and does what he believes Ender Wiggin, the first Xenocide, would have done even if he knew that he was actually destroying the Formics, not training, and fires the M.D. Device. He further misjudged that thinking he was protecting all human life from the descolada even though it was eradicated and replaced by the recolada, so all species could live naturally on Lusitania.
However, Jane is granted possession of Young Val's body, so she is not destroyed by the ansible shutdown. She is then able to continue transporting starships instantaneously creating a path way for her aiúa along the simple-minded large pequenino mothertrees who have ample memory to spare. She is then able to get Peter and Wang-Mu close enough to the M.D. Device so that she can find her way back and transport the Molecular Disruption Device itself to the Lusitania fleet, where it is then disarmed and disabled.
Ender's aiúa leaves his broken, old body and previous life behind to live in Peter, Jane falls in love with Miro, and Peter with Si Wang-mu (Both couples get married under one of the mothertrees of the pequeninos, the same day as Ender's funeral), Peter's efforts finally come to fruition, and the destruction of Lusitania is averted. The story ends with the two new couples being taken to the Outside by Jane herself and back In to an unknown destination.