
Empty World is a novel written for young adults about a virus that wipes out almost the entire human population. Like John Christopher's fiction for adults it offers a fairly bleak view of human nature, but as Puffin don't usually publish novels with gang rape scenes (with the possible exception of Melvyn Burgess), the drama is a little more restrained.
As with everything written by Sam Youd (John Christopher's real name), Empty World is an enjoyable work of escapist fiction that is consistently gripping and thoughtful. The average customer review on Amazon is five stars - a rare accolade for any novel - so why is it out of print?
The simple answer is that however good a novel is, unless it is heralded as a great work of literature or the author is commercially successful, it will probably go out of print.
When I worked in bookselling I remember the dreaded acronym RPUC - reprint under consideration. At first I used to convey this information to customers, who would then plague me for months, to the point where I had to hide in the stock cupboard until they left. I soon realised that RPUC was as good as OP - out of print.
It's depressing seeing a much-loved book fade into obscurity, but the beauty of the internet is that readers now have a voice. I have no doubt that Penguin's decision to reissue John Christopher's The Death of Grass has something to do with the huge demand for secondhand copies on the internet. As for Empty World, I'm sure that it will sell if only someone can come up with a better jacket than this:

The artist, David Chestnutt, has produced some highly-acclaimed psychedelic record covers, but this illustration looks like he's had some bad acid.