The story of Sarah Edmonds is a fascinating one for many reasons. She escaped an arranged marriage by disguising herself as a man and crossing from Canada to the U.S., ending up in Michigan in time to fight in the Civil War. Her lack of facial hair made her look even younger, so her first effort to enlist was refused, but later she managed to serve, under the name Frank Thompson. Then, as Frank, "he" became a nurse and a spy, an ongoing master/mistress of disguise, crossing enemy lines as everything from a black man to an Irish washerwoman.
Like other women who served as men in wartime, life was difficult, but this short book mainly covers the interesting parts. This is a short overview, not a detailed biography, but it's very good for what it is.
The end notes and bibliography are very good, and lead those interested into further reading.