I loved this book when i read it, many years ago. I can still remember what it was about, so it must have made a impression. Basically it is the story of how a time machine, designed to bring back extinct animals, attracts the attention of some very unsavoury individuals.
I would recommend this book for 9-12 year olds who want a good read, though it will be especially apreciated by sci-fi fans.
Perhaps not the most subtle book, it raises questions about the uses and abuses of science in a way accessible for children.