William Pène du Bois' fantastic story. I regret that I am undoubtedly unable to convey this sufficiently, but hope to interest you enough that you may seek it out and read it!*
The three policemen live, along with a number of other happy people, on a mysterious and rather unknown island called Farbe. So happy are the Farbons, who are all fishermen except for the three policemen and their aide, Bottsford, that there is no crime. Ever. It is for this reason that the policemen's mettle has never been tested! In fact:
"In their spare time, which is almost anytime, the three policemen design and make their own uniforms, which get more and more elaborate. This seems to be their only work." (p. 10)
Here are the policemen readying themselves in the morning:
Inevitably, crime does come to Farbe Island- one morning, all of the fishing nets are stolen! The islanders gnash their teeth and pound the earth in very dramatic despair:
A meeting is called; witnesses reveal that the culprit is... a sea serpent!
They board the ship, and when sailors cut the heads off the 'fish', they spring out!
The inside dust jacket reveals a cross-section of the sea-serpent boat: