In short, get this book if you are needing to get started in PR as part of your job, or are a beginner as a PR specialist.
My first PR job was at a nonprofit with no money for 'real' PR. This book helped me use the few dollars we had without comprosing quality required to make a good impression to publications.
It explains the basics, what make a good PR person, and how to pull together the job of convincing others to cover your stories. How to get pics published, media visits, controversy. Logically written, it outlines options and reasons for responding to various situations.
A great asset.. this book has a solid directory of resources to help you get your job done.
No essential is left without guidance. However, missing from it is a "new" essential, the web. Maybe a newer edition will come out to cover this?