This book, Treason's Harbour by Patrick O'Brian, is definitely the second of a story arc. I complained a bit about the end of the last one, The Ionian Mission, and this book picks up a few weeks later. French agents are operating in Malta and try to use a young woman, Mrs. Fielding, who's husband they have captured, to get information from Maturin. Maturin, being a bad ass secret agent, see through this ploy and with Mrs. Fielding's help begins to feed the French false information. There is a chink in Maturin's invincibility though as he fails to see a real traitor operating at a high level in the Navy. Aubrey is more in the background in this book but has an amazingly funny scene where he rescues Mrs. Fielding's large dog. There's also a long section where all the Surprises go overland to the Red Sea for a mission, which has both hilarious and dramatic moments. a 5.
I would have the same complaint about the end but i had already picked up the next book and just took out the last disc of this one and put in the first disc of The Far Side of the World this morning driving to work. I can't imagine (ok, well i can *cough*Martin*cough*) how frustrating reading this series as it came out must have been. O'Brian got them out at a pretty good clip: 20 books in 30 years is not at all bad! Overall i really can't recommend this series enough. It is wonderful!
If you want to read Jo Walton's takes on these novels, Tor.com is running them here. They are highly spoilery, to the point that i think i am going to stop reading them until i finish up the series.
The Literate Man is also hosting a challenge to read the series by the end of the year. i really should join but i did start in November 2010.