Blue At The Mizzen: Patrick O'Brian

Book XX of Master and Commander. After Waterloo, Jack and Stephen set sail on a mission to Chile. Under the guise of a merchant vessel, their real mission is to aid the Chilean struggle for independence. There is near-shipwreck, infidelity, the capture of a pirate ship and the siege of a fortified harbour to contend with - and Jack's longed-for promotion to Rear Admiral of the Blue seems further away than ever.