American spies discover the Chinese have built a weapon capable of destroying planet Earth, a "doomsday machine" if you will, and that they plan to use it within a matter of days. Will the human race survive?
Captain's daughter Josephine and common sailor Ralph Rackstraw are in love. However, their relationship is complicated by her arranged marriage to the high-ranking Sir Joseph Porter. A secret about the characters' true identities revealed by Little Buttercup, which leads to a farcical resolution.
