Maturin is feeling burnt-out, so a cushy job is arranged for him. Aubrey is to command a ship heading to Botany Bay to deal with troubles facing Governor Bligh, but the real purpose of the mission is for Maturin to get chummy with a beautiful American spy who is being transported there. An iceberg intervenes.
Aubrey and Maturin head back to England - but are interrupted by another disaster at sea and the outbreak of the War of 1812. The pair find themselves witnesses to and participants in not one, but two, of the famous single-ship actions of that war and are held prisoner in Boston. Maturin meets an old friend, but his cover is compromised.
The pair are feted as heroes on the North America Station (Aubrey forming an unfortunate entanglement), but finally return to England (where Aubrey's troubles with a landshark and a powerful enemy in the Admiralty are beginning to bite). A confidential mission in the Baltic proves successful, but Biscay weather leads to capture and imprisonment by the French.
We're now well into 1812, which famously for O'Brian contains 60-odd months (he was running out of war and had a lot to fit in!).
Aubrey is now given command of an aged line-of-battle ship and has to contend with the tedium of close blockade (of Toulon). Things are livened up though when he is reunited with his old love, HMS Surprise, and the pair and a hand-picked crew are sent to the Ionian Sea to meddle in the politics of the semi-independent states there.
If not a lot happens in The Ionian Mission, O'Brian makes up for it in Treason's Harbour!
The pair and the remaining Surprises are ashore in Malta, which turns out to be a hotbed of intrigue. For once Maurin is the subject of espionage rather then pulling the strings himself. He falls foul of a French spymaster and a high-level traitor.
Having been told for several books that Aubrey is now too senior to command a frigate and that Surprise is too old and small to face up against the Americans, Aubrey is now sent in Surprise to intercept an American frigate heading out to the Pacific, where it will otherwise be unopposed in cruising against British whalers.