This is book 6 of the "Aubrey-Maturin" series.

This note contains spoilers for the book.

Let's see; Jack manages to bring the horrible old Leopard back from Desolation Island, and surprises everybody. He and Stephen are sent back to England in a despatch boat, but through a series of accidents they end up taken by the Americans, and carried to Boston as prisoners.

They lodge in a mad hospital, run by a competent and charitable doctor. To the madmen that are their neighbors are added visits from American naval officials and intelligence officers. Because people suspect that something happened involving Aubrey or Maturin that brought false information to the Americans for the French. There are in fact some French officers present.

Stephen narrowly escapes being captured or killed a few times. In the end he kills the French officers, and takes off with Aubrey and Diana (who had gone to America with Mr. Johnson, you may recall) in a small boat to be picked up by the British squadron blockading the harbor.

In this fashion they end up aboard the Shannon when she fights and takes the Chesapeake, reversing a long and completely devestating series of naval defeats (something the Royal Navy has not previous suffered).