It's not easy being a heroine inside a story that no one is reading.But Princess Sylvie has an even bigger problem: By chance, she and the other characters from The Great Good Thing and Into the Labyrinth find themselves launched into outer space bound for the moons of Jupiter! Here they must learn to act out their book's plot while floating weightlessly through the pages.If life is bizarre for Sylvie, it turns grim for the astronauts when their spaceship misses reentry to Earth's atmosphere. Equally disastrous, the aging process has somehow reversed itself, regressing the crew toward babyhood. Birth, death, and infinity become fatally intertwined. What, from inside her book, can Sylvie do? How can she save the doomed ship, the astronauts she has grown to care for, and even the book she lives in?