Earl Wayland Bowman

Following a rift with his wealthy father, Billy Mathewson, a young Broadway wastrel, escapes with his friend, Dizzy Durby, to the small town of Salino, where his father's company is building a dam. However, a crooked foreman is engaged in making himself rich at the expense of his employer and the villagers. However, Billy defeats the villain, and also wins Elinor, the daughter of a prominent local resident.

In the waning days of WWI, a U.S. "Mystery Ship," sets sail for the coast of Spain towing a submarine. Their mission is to find and sink a U-boat that has been especially effective in attacking Allied shipping. Posing as a harmless schooner, the mystery ship is in fact fitted with a formidable gun capable of sinking a U-boat. Stopping in the Canary Islands to refuel, the crew interacts with locals involved with Germans, and with Germans themselves, including the sister of the U-Boat commander, who is lurking offshore waiting for the coming battle.