A man wakes up from a dream-like state, naked and freezing, with no memory. A little girl leads him through a series of corridors in a generation ship in search of warmth. She calls him Teacher, and together they encounter several other strange beings as they travel through the ship trying to survive and find the answers to their questions.
Teacher eventually finds out that he is a clone and has been resurrected several times before, although those versions did not survive. Each clone was able to leave bits of information, a kind of breadcrumb trail for the next iteration. It is from these diaries that Teacher discovers the true nature of his situation. His companions are clones as well, genetically engineered for specific purposes.
The ship's crew has separated into two groups, each vying for control of the ship. One faction wants to abandon their mission to colonize a planet which is already teeming with life, while the other wants to press forward. The ship is damaged during one of their battles, and the clones have been created in order to fix it.
Teacher, who discovers his real name is Sanjay, eventually reaches the third hull of the book's title where he encounters Mother, who is the leader of the faction that wants to continue to their destination. She tells him she created him to be her ally. In the end, Teacher and his companions flee from Mother and await their arrival on the new planet.[2]
