Crown Publishing Group offers, on their website, free _ "Reader's Guides" for nearly 300 of the books that they publish. These guides are similar to the famous _Cliff Notes_.
Here's the URL:
http://crownpublishing.com/readers-guides.
Crown is an imprint of Penguin Random House. I have not yet perused the websites of Crown's sister companies to see if any of them offer such reader's guides. Stay tuned.