From the webpage:
The entire Pro Git book, written by Scott Chacon and Ben Straub and published by Apress, is available here. All content is licensed under the Creative Commons Attribution Non Commercial Share Alike 3.0 license. Print versions of the book are available on Amazon.com.
Available on the web, in PDF, mobi, or ePub form for free and in a variety of languages.
At five hundred and seventy-four (574) pages I suspect it covers any subtlety of Git that you will need.
Pass this along!