The Ionian Mission — Patrick O'Brian

Jack Aubrey and Stephen Maturin, veterans now of many battles, return in this novel to the seas where they first sailed as shipmates. But Jack is now a senior captain commanding a line-of-battle ship in the Royal Navy's blockade of Toulon, and this is a longer, harder, colder war than the dashing frigate actions of his early days. A sudden turn of events takes him and Stephen off on a hazardous mission to the Greek Islands, where all his old skills of seamanship and his proverbial luck when fighting against odds come triumphantly into their own.