Marriages Are Made (1918)

Cyrus Baird is trying to force his daughter to marry Ethelbert Granger, wealthy but effeminate. She meets and falls in love with James Morton, nephew of Baird's pet enemy. Ethelbert takes the Bairds to cruise in the houseboat of Max Rupholdt, who has a mine layer concealed in the innocent looking craft. Morton, suspected of disloyalty, penetrates Max's secret and rescues the girl just before the fleeing spy meets extermination through one of his own mines.