A synopsis is a brief overview of your book. It's usually one page but some writers will write a two page synopsis. You don't give everything away in a synopsis. I have information on how to write a "film synopsis." Here's an excerpt that could be applied to your book -- just substitute "film" for "non-fiction" book.
You need to create a document of no more than 1-2 pages (single-spaced) that accurately set up the time, the location, the high points of your story, including how it resolves.
1. Write a brief narrative to give the setting and background to your potential film (book). Use clear and simple language. Keep it to a few sentences, giving the reader a feel for the film without details. Depict the physical setting and when the film takes place, whether it's today, 20 years ago or 200 years in the future.
2. Describe in as few words as possible the main plot and how the main character is involved. Leave minor characters out unless they help propel the story. Make sure it has a beginning, middle, climax and end.
3. Use only details that are important to the plot and won't require too much description. Try to incorporate these details into the description of the plot, if possible.
4. Finish your synopsis with a clear idea of how the film ends. Leave the reader satisfied, yet wanting to know more.
5. Type your synopsis double-spaced and proofread it for spelling and grammar errors before sending it to a producer. You don't want to appear unprofessional.
6. The synopsis is what sells the editor on the manuscript. If Agents don't see anything they like in the synopsis, they won't even glance at your chapter samples.
I hope this helps.