In the British garrison in Singapore, Captain Robert Anstruther discovers the possibility of an affair between Lady Costabel, the wife of his Colonel, and Lord Ventnor. While the Colonel is away, Robert's orderly is killed by Ventnor's servant, as he searches for evidence of the affair. After the Colonel returns and Ventnor's cap is found in Lady Costabel's boudoir, Ventnor convinces her to claim that he stopped Robert from annoying her. Rather than destroy Lady Costabel's reputation, Robert remains silent and is cashiered from the service. Under an assumed name, he works as a sailor, and during a shipwreck, saves Iris Deane, the owner's daughter. Alone on a desert isle, Robert and Iris fall in love. While they are fighting off pirates, her father's rescue party, including Ventnor, now Iris's suitor, finds them. Ventnor denounces Robert, but in Singapore, Lady Costabel, feeling deceived by Ventnor, confesses to her husband. Robert is restored to the service, and he and Iris spend their honeymoon on their desert isle.