One-Eyed Jack, great-great-grandson of that notorious pirate, Black Jack, hijacks a battleship, but he then has to face that internationally-famous detective, Inspector Willoughby in a battle of wits. Hopping into his outboard motorboat, he puts One-Eyed Jack under arrest, but One-Eyed Jack promptly sinks him and his boat with pistol fire. One-Eyed Jack laughs, but Willoughby arrests him again from the conning tower of a submarine. One-Eyed Jack sinks him again with a well-aimed cannonball. Willoughby boards the battleship and threatens to use force if One-Eyed Jack doesn’t come along. This amuses One-Eyed Jack, but Willoughby whips him about violently. One-Eyed Jack loads him into the cannon again, but it won’t fire. Seeing a big cork in the muzzle, he tries to pull it out. Willoughby fires the cannon, sending him over the horizon. Back fast in a rowboat, One-Eyed Jack puts Willoughby in a sea bag and throws him overboard. Finding Willoughby standing beside him, he pulls the bag up and finds Willoughby in the bag. Puzzled, Willoughby has One-Eyed Jack get into the bag to show him how it’s done. He throws the bag overboard, and hammerhead sharks give him a beating. Willoughby pulls up, but he gets thrown in the bag and overboard again. Seeing Willoughby standing beside him, One-Eyed Jack pulls the bag up and finds a ticking mine. Running with it, panic-stricken, Willoughby shows him to the powder room. The explosion shoots One-Eyed Jack into a lifeboat, where Willoughby, as coxswain, orders him to row to shore, towing the battleship.