I would call this the "everything you wanted to know to get started with Lucene in 70 pages" book. True enough, in a mere 70 pages the authors give you enough information for you to understand the basic Lucene workings and make you feel like jumping into action and starting to do something with Lucene. In addition to that, the book simply throws some gems in there that pretty much solve the issues you would hear mentioned over and over in the context of search engines. Wildcard searching, search optimization, multiple language support (analysers in detail), highlight snippets, search within search, Latent Semantic Indexing, common document formats indexing (PDF, HTML, XML, RTF)...you name it, they probably put in there.
A fundamental read if you want to know what Lucene is all about. Even more if you actually need to use it! A really good read!