Sharpe's Fortress by Bernard Cornwell

Sharpe's Fortress is the third (historically) of the Richard Sharpe series, and last of the Sharpe India trilogy, by English author Bernard Cornwell. It tells the story of ensign Sharpe, during the battle of Argaum and the following siege of the Fortress of Gawilghur in 1803.

The explosive grand finale of Richard Sharpe's adventure in India finds the defenders of the fortress of Gawilghur standing between Sharpe and his reputation, his honor, and a sultan's stolen jewels.