Jack Diamond and his sickly brother arrive in prohibition New York as jewelry thieves. After a spell in jail, the coldly ambitious Diamond hits on the idea of stealing from thieves himself and sets about getting close to gangster boss Arnold Rothstein to move in on his booze, girls, gambling, and drugs operations.

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.