In this adventure the diplomatic free-lance and his brilliant aid in war, Nan Tremain, are again pitted against their relentless enemy, Pfaff. England and Japan have entered into a secret treaty, and extraordinary precautions are taken to prevent anything about it leaking out. The Marquis Yato, the Emperor's diplomatic adviser, brings the treaty from England, but comes in the guise of a captain of a cruiser which forms part of a squadron dispatched to Great Britain. The arrangements are that the message shall be delivered to a cabinet minister. Lord Faresdale, whose comfy home is near Clovelly, where the squadron is to anchor. Lord Faresdale goes aboard the cruiser, receives the copy of the treaty and then places it for safe-keeping in a safe in his library. In some way Pfaff has learned about the treaty and just the manner in which it would be delivered. Two of his spies are in Lord Faresdale's home as guests, one an Austrian general and the other a young noblewoman. These two dragged into the plot Capt. Mandeville, an Englishman, who is in love with the girl. By tricking him in cards and telling him false stories concerning Lord Faresdale, they secure his aid, he believing that the package he is to steal from the safe contains love letters foolishly written by the noblewoman's sister. Fortunately for the cause of England, Lord Trevor and his ward are at Faresdale's house during this time and their suspicions become aroused by certain peculiar incidents. In the end the diplomatic free-lance and his ward give aid in the nick of time and even Mandeville, the poor cat's paw, did not suffer while Pfaff and his conspirators are driven from the field.