Captain Aubrey and Doctor Maturin are going to South America on a secret mission on the Surprise, but plans suddenly change. Aubrey is urgently restored to the lists of the fleet, he receives command of the frigate Diana, which he had captured, and together with Maturin they set off for the eastern seas with a diplomatic mission and a royal envoy on board. Once (in the third book) they no longer made it Mr. Stanhope there. The purpose of the voyage is an agreement with potential allies of England in those parts, and there are already the French and the traitor Ray. Maturin finds himself in a naturalist's paradise... And an unexpected adventure lies ahead.