The Mate of the 'John M': Jim, the mate of the ship "John M.," is in love with Mandy, the daughter of Captain Dale. Before she leaves for boarding school, she hurries to the ship to say good-bye to it, her father and Jim. Six years have now passed, and Mandy has grown to a big and handsome girl. As Captain Dale is going to make another trip, Mandy asks him if she cannot go along. Mandy's school chum's brother wishes to go also, and the Captain gives his consent. Jim grows a little jealous at the young man's presence on board.