"A Tom Doherty Associates book."

"Seventeen-year-old Lake seeks the secret heart of the computer simulation that safeguards passengers aboard a ship orbiting a post-apocalyptic Earth, on a quest that will either save or destroy them all." --,(Source of summary not specified)

The Earth's survivors escaped into a passenger ship orbiting Earth. Their minds were put in a simulation designed to prepare them all for life after the nuclear event, but some are trapped in a shared virtual reality, their bodies in stasis chambers. No one can get off the ship until all the passengers are out of the sim. Time is running out, and as Lake searched for the heart of the sim, her ally Taren is deciding who must be sacrificed for the greater good. -- adapted from jacket