Sylvia Donovan, Roy Donovan, and "Count Donelli" are three international crooks who come to America. Sylvia and Roy are unaware that they are brother and sister. The three cooperate to rob wealthy homes by using a gimmick known as a chess-playing machine. Eventually, Sylvia and Roy learn that they are brother and sister and that "Count Donelli," alias Hawkes, killed their father. The detective and Sylvia fall in love.