Natty Gann is a 12-year-old Depression-era girl whose single father leaves her behind in Chicago while he goes to Washington State to look for work in the timber industry. Natty runs away from the guardian she was left with to follow Dad. She befriends and is befriended by a wolf that has been abused in dog fights, hops a freight train west, and is presumed dead when her wallet is found after the train crashes. Dad gets bitter and endangers himself in his new job. Meanwhile, Natty has a series of adventures and misadventures in various farmhouses, police stations, hobo camps, reform schools, and boxcars.