An anarchist plot to blow up King George V is foiled by Lt. Rose. Lt. Rose is called in by his captain and is shown a letter from the local Commander expressing concern at the influx of 'aliens of an anarchist type' into the area scene the announcement of a visit by the King. With a midshipman to assist him, Lt. Rose goes ashore in plain clothes. The two go to a restaurant where they see a large number of anarchists going through to a back room. Discovering a trap door, Rose descends to the cellar and climbs a ladder to listen to the anarchists plotting in the room above. Their intention is to plant a bomb under the pier [One of the spies is named Johann]. Having altered the local police, Rose hides on the pier and watches an anarchist plant a bomb under the pier. After the anarchist has gone, Rose removes the bomb and drops it into the sea. He follows the anarchists and locates their hideout in a hut at the foot of the cliffs. Moving closer to the hut, Rose overhears their plan to blow up the King's ship if the first bomb does not go off. The King arrives on the pier and inspects the troops there. From the hut the anarchists observe the failure of their first attempt and set off in a boat to launch their backup plan. They go by boat to the pier head where a diver is lowered followed by the bomb. Rose also sets off by boat and dives. The two divers meet and fight at the sea bottom. The anarchist is overpowered and stabbed by Rose, who cutting the two airlines, switches so that he is pulled up into the anarchist's boat where he overpowers the men before ramming the dinghy with the rest of the anarchists in it. Rose reports back to his Majesty's ship where he is presented to the King.