Peter Duck [Swallows and Amazons #3]

Peter Duck is the third book in the Swallows and Amazons series by Arthur Ransome. The Swallows and Amazons sail to Crab Island with Captain Flint and Peter Duck, an old sailor, to recover buried treasure. During the voyage the Wildcat (Captain Flint's ship) is chased by another vessel, the Viper, whose piratical crew are also intending to recover the treasure.