Lieutenant Rose is seen in a bar talking to a woman. He invites her and her friend (who is not present) to visit his battleship. The woman, who is a spy, meets up with her comrades bringing disguises for them. The woman, together with a man disguised as a woman and a man disguised as a boatman are greeted at the ship by Rose. He leads the two women onto the deck and shows them the ship. On the bridge a signal is received. The party appear on the bridge. An officer enters the captain's cabin and retrieves the signal book from the safe. On the deck he translates the message. However, one of the women falls down, as the officers rush to her aid the other women takes the book replacing it with a copy. The officer returns the book to the safe and the women leave the ship. Later the captain receives a message and he uses the book in order to decode it. However, he cannot. He calls in the other officers and they realise that the book has been stolen by the women. The captain orders the battleship to open fire on the row boat, however they miss. Rose is sent ashore with a party of sailors and they give chase. During the chase one of the spies disposes of the book in a pond. Rose and his sailors capture the spies. However one spy escapes, he retrieves the book and makes off. Rose and the captured women return to the ship. The captain on the bridge orders the ship to fire on the enemy battleship. [Presumably the spy with the book has escaped onto the ship]. The ships open fire on each other.