Sharpe's Devil by Bernard Cornwell

Sharpe's Devil: Richard Sharpe & the Emperor, 1820-1821 (Richard Sharpe's Adventure Series #21) - In the years since Waterloo, Sharpe has been living in Normandy with Lucille.  Don Blas Vivar's wife comes to Sharpe, requesting that he find her husband in Chile.  As they cross the Atlantic, Sharpe's ship stops at St. Helen's to visit Napoleon.  In Chile, Sharpe and Harper find that Vivar has been killed and buried.  Although given permission to travel in Chile and exhume the body, Sharpe is imprisoned.