While Lt Daring visits a houseboat, it is suggested to him that he might like to have his portrait painted. However, the artist is a secret agent and, during the first sitting he and his female assistant overpower Daring and leave him bound and gagged.

Daring's dog, Nero, manages to release his master, but the agents have already boarded the Continental express. Daring attempts to catch the train but his car breaks down. He runs to an airfield and borrows a biplane and gives chase.

The spies disembark from the train at Folkestone and board a passenger steamer. Daring lands at Folkestone, and finds that the agents have already boarded the steamer and that it has left. Undaunted, he follows in a launch and catches the steamer and boards. Disguised in a coat, he observes the agents. In Boulogne, he asks two policemen to arrest the agents and then proves his case by revealing the stolen plan of the minefield on the lady's back. He is taken to a café by French sailors and all celebrate his success.