Lieutenant Gilbert Maltravers is bored. It is 1912 and he has been promoted as fast as any in his Dartmouth class and is placed in a battleship where he can confidently look forward to promotion to post captain and a battleship of his own by the time he is forty. All he needs to do is keep a smart ship, polish the brass and salute every senior officer, while wearing an expensive uniform that testifies he is one of the right sort. His father is an admiral, so very little can go wrong.
He wants more than tedium from his existence, and the new submarine service will provide excitement . . . but possibly a far shorter life. If he is successful, then submarines will provide earlier promotion and a new challenge every day. Failure in the submarine service will mean the end of his career.
Against the protests of his father and the head-shaking of his friends, Gilbert goes off to join the deplorably new and ungentlemanly assassins of the sea, the enemies of all the old Navy stands for.