Edmonds' interest in adventure was sparked in childhood by
Maturin Murray Ballou's book
Fanny Campbell, the Female Pirate Captain, telling the story of Fanny Campbell and her adventures on a pirate ship during the
American Revolution while dressed as a man. Campbell continued dressing as a man after the war in order to pursue other adventures. Edmonds used Campbell as an inspiration to "escape the limitations of her sex." She at first served as a field nurse, participating in several campaigns under
General McClellan, including the
First and
Second Battle of Bull Run,
Antietam, the
Peninsula Campaign,
Vicksburg,
Fredericksburg, and others. According to her memoir, Thompson's career took a turn when an American spy in
Richmond, Virginia, was discovered and put before a firing squad, and her friend James Vesey was killed in an ambush. Thompson took advantage of the open position, as well as the opportunity to avenge Vesey's death, and became a spy. There is no proof in her military records that she actually served as a spy, but she wrote extensively about her experiences in her memoir. Thompson suffered an injury before the Second Battle of Bull Run in 1862, when she took a trip to
Berry's Brigade in order to deliver mail. In an attempt to take a shortcut, she was thrown into a ditch by her mule before reaching the brigade; she sustained severe injuries. In 1863, she contracted
malaria. Doctors urged her to go to the hospital for treatment. Thompson abandoned her post in the army, fearing that she would be discovered as a woman if she went to a military hospital. She checked herself into a private hospital, intending to return to military life once she had recuperated. Once she recovered, however, she saw posters listing Frank Thompson as a deserter. Rather than return to the army under another alias or as Frank Thompson, and risk execution for desertion, she decided to serve as a female nurse under her real name at a
Washington, D.C. hospital for wounded soldiers run by the
United States Christian Commission. There was speculation that Thompson may have deserted because of John Reid being discharged months earlier, and there is evidence in Reid's diary that she had mentioned leaving before she had contracted malaria. Thompson's fellow soldiers spoke highly of her military service, and even after her disguise was discovered, they considered her a good soldier. She was referred to as a fearless soldier and was active in every battle that her regiment faced. ==Memoir==