Candy Smith-Foster is 11 years old, a karate black-belt, and a new breed of genius. That's useful, because the world has ended -- everyone else is dead from the plague caused by the biowar. So she sets off to find out if she really is alone, keeping a detailed journal of her travels and experiences. But the end of the world turns out to be the least of her problems.
The compressed syntax of Candy's journal takes a while to get used to -- say about a page -- after which it provides a great flavour to all the wry, smart, cynical, pragmatic observations. Then towards the end of the book, other viewpoints give us the chance to view Candy from the outside as well, and to contrast that with the view of her we get from her own account. The plot rips along, remorselessly sucking the reader in to more and more improbable events, until the mind-boggling finale seems like a natural and obvious result.
If you set your willing suspension of disbelief to 'high' (the shuttle wasn't that bad, really, but the kodiak bear was going just a bit far...), and if you like Heinlein-esque juvenile geniuses, you should love this. Possibly the best Heinlein juvenile Heinlein never wrote.