The plot assumes that ships could land passengers at St. Helena in 1820 to interview Napoleon. Such was not the case. The British fired on any unauthorized ship attempting to approach the island including, in one case, a ship in distress. Other than that, it is an interesting tale.
This is the last novel, chronologically, in the Richard Sharpe series. Sharpe is separated from his wife and living in France with his latest mistress and their two children. His shortage of money indicates his wife in England has everything he stole in Spain. When the Countess of Mouromorto shows up to hire Sharpe to find her missing husband in Chile, his mistress is very receptive to the sight of the money (needed to improve her farm). Sharpe finds himself on his way to Chile with his old friend Patrick Harper, and makes the aforementioned stop at St. Helena to see Napoleon.
Sharpe and Harper become involved, unwillingly, in the civil war raging in Chile between the Spanish royalists and the rebels under O'Higgins (supported by Lord Cochrane). Sharpe's fortunes take some twists and turns, as does the plot. The involvement of Lord Cochrane in Chile is described fairly accurately, including the action at Valdivia. Sharpe, of course, gets his share of the spoils. One can hope that Sharpe will fare better with his latest mistress than he has with earlier women in his life. Having Sharpe acquire bags full of loot always creates the possibility of further action (after all, Lord Cochrane did invite him to go along, and we know from history that Lord Cochrane later served in Brazil and Greece).