The Surgeon's Mate
Patrick O'Brian
 The Surgeon's Mate starts in Halifax, Nova Scotia. Jack Aubrey and Stephen Maturin, having escaped from the Americans in Boston aboard , start their return journey to England aboard a packet ship. Two American privateer schooners — commissioned by Harry Johnson, an American spymaster — doggedly pursue the packet ship across the Grand Banks until one of them fortuitously hits an iceberg. On their return to England, Stephen receives an invitation to speak at the Institut in Paris on the extinct avifauna of Rodriguez Island and he and Diana visit the city. Stephen arranges for Diana, who is pregnant with Johnson's child, to stay with a friend Adhemar de La Mothe for her lying-in. The British Admiralty is keen to capture the fortress at fictitious Grimsholm Island (distinct from the Grimsholmen nature reserve) owing to its highly strategic location in the Baltic. Maturin, accompanied by Jack Aubrey and Jagiello, a remarkably talented and handsome young Lithuanian, embarks on a mission to persuade the Catalan garrison of the fortress to defect. Aboard , Aubrey manages to capture the Minnie, a swift Danish privateer cum merchantman, after a day-long chase. Once Stephen Maturin and British hands are aboard, they pretend to give chase to her in order to deceive the Spanish garrison. Maturin is eventually landed and, in the absence of any French officers, warmly welcomed by his Catalan godfather, Ramon d'Ullastret. The next morning, the Catalan troops and their colonel are loaded aboard the transport ships and the successful expedition receives a warm welcome back at base from Admiral Sir James Saumarez. Caught up in a storm in the English Channel, the Ariel spots pursuing a French two-decker, the Meduse. Aubrey decides to help the chase and blasts the Meduse with his carronades without suffering much damage, slowing her pace enough for the Jason to gain. After losing sight of them, the Ariel is caught up in two nights of dark, stormy weather and finds herself fifty miles off course with the wind dead on shore. Aubrey attempts to club-haul her but the Ariel ends up beached on the shore. After a brief period of imprisonment in Brittany, Jack, Stephen and Jagiello are taken to Paris, accompanied by a Monsieur Duhamel. Imprisoned in the Temple prison, Aubrey attempts to break out down the immense stone privy as Stephen is interrogated by French officers, who represent a different intelligence agency than Duhamel's. In the meantime, Duhamel has approached Stephen with an offer to take peace offerings to the King and British government (presumably a plan hatched up by Talleyrand and some senior officials). Duhamel also gives Stephen some English newspapers to read and Jack's spirits are buoyed to learn from the Naval Chronicle that defeated the Meduse in the action which beached his ship, the Ariel. Stephen's second interrogation is interrupted by the American, Johnson, who is able to identify Maturin as an intelligence agent and the killer of French spies, Dubreuil and Pontet-Canet. This action places Maturin in great danger. It also turns out that Diana Villiers has given her great diamond, the Blue Peter, to a Minister's wife to help secure their release. Just as Jack breaks through the privy, four Frenchmen enter their prison cell — D'Anglars, Duhamel, a foreign ministry official and a cloaked officer. After agreeing terms, the prisoners are taken down to two carriages and spirited out of Paris (accompanied by Diana who has lost her baby) to a waiting cartel at Calais, the Oedipus commanded by William Babbington. Safely away, Stephen proposes to Diana Villiers once again and they are finally married on board by Babbington, with Jack giving her away. The book title is a triple entendre in its use of the term "mate", referring to a ship's surgeon's assistant, a chess reference to Maturin's successful espionage efforts (i.e., checkmate), and Maturin getting married at the end of the story.