The Constellation of Sylvie - Roderick Townley

In Roderick Townley's The Constellation of Sylvie, the characters of The Great Good Thing are feeling a little bored as not much has happened since their adventures on the Internet (in Into the Labyrinth). But they will shortly find themselves facing worse danger than they've ever faced before when their book is stowed away on a space shuttle before it embarks on a four-year mission to Jupiter. At first, the characters' main difficulty is adjusting to life in zero gravity, but then the shuttle misses its re-entry window into the Earth's atmosphere, and Sylvie and the others are forced to find a way to help the astronauts survive their additional four years in space. The solution comes in the form of ice collected from one of Jupiter's moons as melting and evaporating the ice provides enough oxygen to sustain the shuttle crew. Unfortunately the ice also contains a compound that has a very drastic side effect: the astronauts' ageing process is reversed until they are only children, and their lives, and the fate of the characters lie with Sylvie, who must reach into the dreams of the astronauts to help them make it back to Earth alive.

I confess I cried at the ending of this book (which I read in 90 minutes flat in bed, because I simply couldn't put it down) - I won't say more because this isn't the Spoiler Zone. I recommend Townley's trilogy - the premise of the characters not only being alive, but interacting with their physical environment, and being able to enter the dreams of people outside the book is an interesting and intriguing one.