Born in the shadows of a railroad yard, of a wandering mother who took her lovers where she found them and a father who was scarcely conscious of her arrival in the world, Bertha Thompson took to 'the road' as soon as the restless impulses of adolescence stirred in her. She was more interested in wanders than those who settled down in homes, more interested in criminals than law-abiding citizens. She wanted to see how they lived, live as they did, know what they were like.
As a result of her restlessness and curiosity, she became, in fifteen years of wandering, a hobo, treveling from one end of the country to the other in box-cars, "decking" passenger trains, and hitchhiking; member of a gang of shoplifters, traveling as the mistress of one of the men; a prostitute working in a Chicago brothel; the mother of a child of an unknown father; and a research worker for a New York social service bureau.

Sister of the Road is Bertha's own story of those fifteen years and the record of her conclusions about them. Gifted with a naturally keen intelligence, fearless of consequences to herself, willing and eager to do and be everything which other members of her group did and were, her story is a mine of little-known information and a succession of moving human stories about that vast and growing army of homeless, jobless, wandering women who live by begging, stealing, cheating, prostituting themselves, and occasionally working at legitimate jobs.