The Surgeon's Mate recap

Following their escape from Boston, Jack Aubrey, Stephen Maturin, and Diana Villiers return to Britain. Stephen and Diana marry, while Jack receives command of Ariel for a concealed Baltic operation. Stephen and the Lithuanian officer Jagiello make contact with an isolated Catalan garrison that has turned against French authority, and British naval support allows the men to be removed from danger. On the return voyage Ariel is pursued, forced ashore, and lost; Jack, Stephen, and Jagiello become prisoners and are sent to Paris. French intelligence recognizes Stephen as an agent and subjects him to a more dangerous examination than his naval status would warrant. With help from the disillusioned French officer Duhamel, the prisoners escape and regain British protection. Jack has accomplished the mission but lost his ship, while Stephen returns to Diana with his intelligence identity exposed to the enemy.

Previously: Jack Aubrey and Stephen Maturin survived the loss of Java to USS Constitution and captivity in Boston. Stephen saved Jack's shattered arm, found Diana Villiers living under the influence of the American intelligence chief Johnson, and learned that Johnson's service was closing around him. With help from local allies, Stephen escaped with Jack and Diana to HMS Shannon. Shannon then captured Chesapeake and carried them toward Halifax. Jack is recovering, while Stephen and Diana have renewed their attachment after years apart.

In Halifax, Jack, Stephen, and Diana are safe under British authority after their flight from Boston and Shannon's victory over Chesapeake. Jack's wounded arm is improving, though the recent action and imprisonment have interrupted his career. Stephen and Diana must now decide whether their reconciliation can become a settled life rather than another temporary escape. Their return passage is still exposed to the Anglo-American war, and Jack again helps meet a maritime threat with the professional confidence that injury and captivity have not diminished. The party reaches Britain, bringing Jack back within Admiralty reach and giving Stephen and Diana the first genuine opportunity to resolve their future together.

Jack, Stephen, and Diana have returned from North America. Stephen and Diana marry, ending the immediate uncertainty created by her flight from Johnson, although their long history makes marriage a beginning rather than a simple resolution. Jack is reunited with Sophia and his family but soon receives another command. He takes the sloop Ariel on a mission whose naval orders conceal Stephen's political purpose in the Baltic. Poniatowski Jagiello joins Stephen as a useful companion and interpreter. Their objective concerns Catalan troops isolated far from home after turning against French authority; Stephen must make contact and find a workable settlement while Jack provides transport, protection, and the appearance of a conventional naval operation.

Ariel has carried Stephen and Jagiello into the Baltic under cover of Jack's naval mission. They reach the isolated Catalan garrison commanded by Ramon d'Ullastret. The soldiers' break with the French leaves them vulnerable to enemies around them and dependent on promises from distant powers. Stephen's political sympathies and knowledge of Catalonia help him establish trust, while Jack must solve the practical problem of approaching, supporting, and removing men from a defended position in restricted waters. The operation succeeds in bringing the garrison out of immediate danger. With the political object substantially achieved, Ariel begins the hazardous return passage, where enemy pursuit and difficult coastal navigation replace negotiation as the main threats.

Stephen and Jagiello have completed their work with the Catalan garrison, and Ariel is returning from the Baltic. French pursuit and worsening conditions press Jack toward a dangerous coast. His effort to preserve the ship and company ends when Ariel is driven ashore and cannot be saved. Jack, Stephen, Jagiello, and other survivors fall into French hands. Because the ship was engaged in a concealed political operation, Stephen cannot rely on being treated simply as a surgeon captured during ordinary naval service. The prisoners are sent toward Paris, while French officials begin separating Jack's professional value from Stephen's potential value as an intelligence source.

The Baltic operation succeeded, but Ariel was wrecked during the return and Jack, Stephen, and Jagiello were imprisoned in Paris. French intelligence identifies Stephen as a British agent and attempts to force information from him. The danger confirms that Johnson's pursuit in Boston was not an isolated episode: Stephen's concealed role is now known to another enemy service. Duhamel, a French officer increasingly unwilling to support the treatment of the prisoners, becomes the means of escape. Jack, Stephen, and Jagiello leave confinement through a covert route and make their way out of France. They regain British protection alive. Jack must account for Ariel's loss, but his secret mission had already achieved its object; Stephen returns to his new wife Diana with his identity compromised and future intelligence work made more perilous.

After Ariel is driven ashore and lost, Jack, Stephen, and Jagiello are taken to Paris. Their captors know that Stephen is not merely a naval surgeon and try to extract intelligence from him, making captivity more dangerous than an ordinary exchange of prisoners. Duhamel, alienated from the methods and politics of his own service, helps arrange their escape. The three prisoners are moved out through a covert route and eventually cross back into British protection. Jack has lost another ship but survived an operation whose Baltic object was achieved before the wreck. Stephen returns alive despite the exposure of his intelligence identity to the French, a danger that will follow him into later work. Diana remains his wife in England, so the book closes with their marriage intact, Jack free to face the official consequences of Ariel's loss, and both friends home but no longer able to assume that Stephen's work is secret from enemy intelligence.