Treason's Harbour (Aubrey-Maturin series, Book 9)

This segment of the Aubrey saga is set in Malta, where the captain's "small, sweet-sailing frigate" is undergoing repairs. The island, however, is swarming with Napoleonic agents, which means that Stephen Maturin must do everything in his power to avert sabotage. A typical O'Brian cocktail of action and intrigue.