After the events of The Letter of Marque, Jack Aubrey is reinstated as a post-captain in the Royal Navy. He and Stephen Maturin are sent on a diplomatic mission to the South China Sea. Stephen gets to indulge in both a great deal of natural history and in behind-the-scenes political intrigue during the negotiations. Soon after their departure from Pulo Prabang, the Diane beaches upon a reef and breaks up during a storm, marooning them on a remote island.
The book stands on its own merits, but it also advances the story that builds throughout the series. Ledward and Wray, the English traitors who nearly brought down Jack, get their comeuppance in a ghoulish way. Stephen, weaned of his longstanding dependence on laudanum, is both sharper and less pleasant. There is plenty of sailing, but very few battles. Much time is spent on land, but little of it in England.