Marsh, a draughtsman in the gun factory of John Durant, is swindled by Edward Pinkney, Durant's general manager, out of the huge royalty to be paid should a gun of Marsh's invention prove a success. Pinkney loves Maisie, but is far outrivaled by Lieut. Somers, U.S.N. Somers also has invented a gun which he gives to be cast by the Durant Iron Works, and which, if successful, will do Pinkney out of his expected graft on the Marsh invention. Pinkney takes good care that the Somers gun is "killed" in the making. He then misrepresents Somers to Maisie and her father, and though Maisie loves the Lieutenant, she feels she must give him up. Accompanied by her mother and Pinkney, she goes in the Durant yacht for a cruise in Turkish waters, formally engaging herself to Pinkney. The Durant yacht hits a mine, and in the rush to leave her, Maisie is trapped in the wireless room. With the water surging up about her shoulders, and every means of escape barred she sends out the S.O.S. signal taught her by Lieut. Somers. The lieutenant, aboard a U.S. cruiser, protecting American interests in Turkey, gets the signal, and arrives at the side of the doomed ship just in time to make a sensational rescue. Here follow a mass of complications as the plot gradually resolves itself to its end.