Young and restless Nick Adams, the only son of a domineering mother and a weak but noble doctor father, leaves his rural Michigan home to embark on an eventful cross-country journey. He is touched and affected by his encounters with a punch-drunk ex-boxer, a sympathetic telegrapher, and an alcoholic advanceman for a burlesque show. After failing to get a job as reporter in New York, he enlists in the Italian army during World War I as an ambulance driver. His camaraderie with fellow soldiers and a romance with a nurse he meets after being wounded propel him to manhood.

Aliens from Outer Space are slowly switching places with real humans -- one of the first being a young man about to get married. Slowly, his new wife realizes something is wrong, and her suspicions are confirmed when her husband's odd behaviour begins to show up in other townspeople.