Sharpe's Devil - Bernard Cornwell

Subtitled Richard Sharpe and the Emperor, 1820-1821 and set predominantly in Chile in the twilight days of Spain's South American Empire, and on one of the South Atlantic's more famous islands, St Helena, Sharpe's Devil sees Sharpe and Harper reunite for one last hurrah. Their mission, to find - dead or alive - old friend, Captain-General Vivar, who has disappeared in Chile in mysterious circumstances. But before the quest begins, their St Helena stop off results in a meeting with their old enemy in exile, Emperor Napoleon Bonaparte....

Not sure what prompted Bernard Cornwell to write it, but it's a cracking good story, as always.

amazon.co.uk link: Sharpe's Devil: Richard Sharpe and the Emperor, 1820 - 1821 - Bernard Cornwell