Gerald Tregarthen, sub-lieutenant of HMS Calder, decides to spend his leave on a small yacht and takes train to Poole, where the craft is lying. On the journey he reads in a newspaper a passage relating to the departure from the Tyne of a powerful cruiser, nominally intended for the Brazilian Government, also a series of reports concerning a mysterious accident to the German cruiser Zietan. At Poole he joins his friend and former school-chum, Jack Stockton, owner of the yacht Playmate.
The same night they put to sea, intending to cross the Channel, but off the Isle of Wight they encounter a dense sea-fog, and the Playmate is run down by a large vessel. Tregarthen is stunned by some falling gear, but is saved by Stockton, and both are taken on board the ship that has run them down.
When Tregarthen recovers his senses he finds himself alone in a cabin. From observation he comes to the conclusion that the vessel possesses astounding speed and that she is heavily armored also that he is a prisoner. At length he is taken into the presence of Captain Brooks, in command of the cruiser Olive Branch. This individual claims that his cruiser is the most powerful vessel afloat, and that it is his mission to exterminate war and secure universal peace, using the super-powerful means at his command to achieve that purpose.
He also informs Tregarthen that, as a British naval officer, he will prove useful to the Olive Branch in her mission, and suggests that the sub-lieutenant should serve on board the cruiser for a period of not more than two years. At the end of that time he will be able to impart the valuable knowledge thus gained to the British Admiralty. Tregarthen is about to refuse, but Captain Brooks reminds him that in any case he is virtually a prisoner, and adds, "Take time to consider the matter. I'll see you at four bells, when I shall expect a positive reply."
Author: Percy F. Westerman
Title: The Sea Monarch
First Published by: Adam and Charles Black
Place: London and Glasgow