Sharpe's Revenge by Bernard Cornwell

Sharpe's Revenge (Richard Sharpe's Adventure Series #10) -  Sharpe's wife has gone to England to find a place to live.  Sharpe is charged with stealing Napoleon's gold. Napoleon himself is exiled to Elba. Sharpe embarks on a trek through France and to Naples to prove his innocence.  He forms an shaky alliance with French General Calvet to recover the gold.