The letter of marque
(Book)

Captain Jack Aubrey has been dismissed from the Royal Navy after a conviction for rigging the Stock Market--a crime of which he was innocent. He is set up as master of a private man-of-war by his newly rich friend, Maturin, a Naval physician who also serves the Admiralty as a secret agent, but the loyalty of comrades cannot alleviate the gloom caused by his removal from the Captains' List. An engagement with an enemy national ship of equal force might help, and intelligence of the imminent departure of a French frigate gives Aubrey an opportunity for such a meeting.