Drupal books are a great way to organize content. Unfortunately, there is no way to control access to individual books by default. Like default forums, it's all or nothing.
The Book Access module adds the ability to set view, edit and delete access control for individual books and all pages therein.
This module has no official release as it needs to be tested. The development snapshot is ready for testing though.
If you're interested in such functionality, install this module and please submit feedback and bug reports.
Thanks to LifeWire for sponsoring development of this module.