The return of NASA's first manned mission to Mars was supposed to be a momentous day. But when the crew loses touch with ground control before entry, things look bleak. Safe after a treacherous landing, the crew emerges to discover the unthinkable—every man, woman, child, and animal has vanished without a trace. Alone now on their home planet, the crew sets out to discover where everyone has gone—and how to get them back—only to discover they may not be as alone as they thought.