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A real submarine was used to film parts of this so-so melodrama -- quite a novelty in the early '20s. Ralph Ince both directed and played the lead. When adventurer John Cromwell (Ince) is shipwrecked, he is forced to join a pirate crew. They use a stolen submarine to loot passing ships and hide their loot in a wreck that sits on the bottom of the sea. There is an explosion in the submarine and the pirates are killed. Cromwell, however, manages to escape with the maps to the treasure. He meets Colonel Hamilton (Thomas McGrane) and his daughter Grace (Aleen Burr), and becomes secretary to James Chipman (Charles McNaughton), who is backing one of Hamilton's horses. Cromwell tells his story to Hamilton, his daughter, her fiancé Chubby Madison (John Butler), and Chipman. Immediately everyone goes in search of the loot -- Cromwell with Hamilton and Madison, and Chipman on his own. Chipman, who has absconded with the maps, locates the submarine before the others do. Cromwell is wounded when he tries to board Chipman's boat. Chipman sets Cromwell, Hamilton, and the rest on an island and fires a torpedo at them from the submarine. It misses, and Cromwell swims to the sub, entering through the torpedo tube. He convinces Chipman's men that their boss does not plan to share the plunder with them. The men revolt and Chipman jumps into the sea, where he is eaten by a shark.