The pearling schooners of a trading firm are being robbed by a mysterious pirate. The son of the owner of the firm (James Alexander) goes to the South Pacific island of Avita to investigate and uncover the pirate's identity, vindicating a man who has been unjustly accused. He also has a romance.

After being fired from his job at a grocer, George, gets a job as a stableboy at a local stud farm run by the Fleming family. He befriends the horse Hotspur who is a favourite to win the Melbourne Cup, and develops a strong whistle which is used to make the horse run fast.