Jack Aubrey wins the Ringle , a Baltimore Clipper, from his friend Captain Dundas, as the Surprise accompanies HMS Berenice back to England, after a stop on Ascension Island for repairs to the Surprise . Maturin first meets with Sir Joseph Blaine, while Aubrey heads home to his family. When Maturin does reach home with Sarah and Emily, he finds his young daughter Brigid in the care of Clarissa Oakes, now widowed. He searches for his wife to correct her misapprehensions, about his judgment of her, and about their daughter. Brigid is not talking yet, though old enough to do so. When Maturin meets Sir Joseph at their club, he learns that the Duke of Habachtsthal, the third conspirator in the Ledward-Wray conspiracy, is aiming back at both of them. The Duke's influence has delayed the pardons of both Clarissa and Padeen. Maturin needs to secure his fortune and his family. Maturin asks Aubrey for the Ringle to move his cash to Corunna and then sends Clarissa, Padeen and Brigid to live at the Benedictine house inÁvila, Spain, for safety. Brigid takes to Padeen, and is speaking in Irish and English aboard the Ringle . Both Blaine and Maturin hire Mr Pratt, to gather information on the Duke and to find Diana.
Aubrey gets orders to command a squadron of ships being assembled, a position which earns him promotion to Commodore. The mission to disrupt the African slave trade, illegal since 1807 by British law, is bruited in the English newspapers to be sure the French know of it. The second, secret mission of the squadron is to intercept a French squadron aimed at Ireland, hoping for better success than in 1796-97. Two of the ships in the squadron have captains not up to Aubrey's standards: Duff in HMS Stately has love affairs with forecastlemen, upsetting discipline, while Thomas of HMS Thames is too much concerned about appearance and not enough about seamanship and fighting the ship. Long time friend Tom Pullings is captain of the flagship HMS Bellona , where Aubrey stays and Maturin is surgeon. The Ringle meets the squadron at the Berlings off Peniche peninsula, and the squadron makes its way to Freetown to begin the first mission. The crews practise hard at lowering down boats and other naval skills. Aubrey is in a bad mood, felt throughout the ships, until Maturin tells him that Pastor Hinksey is to be married and set up in India; jealousy had gnawed at him. Aubrey devises a scheme to surprise each slave port up to the Bight of Benin, not touching Whydah, as news of the squadron emptied the harbour. The squadron successfully disrupts the slave trade, saving over 6,000 slaves. They take eighteen slaving ships as prizes, first taking the Nancy , and using the empty ship for target practice to good effect in Freetown. The success is not without loss of men to disease and attack. Maturin survives a bout of yellow fever contracted while out a few days botanizing on Philip's Island with Mr Square. As he recuperates, they stop at St Thomas island for medical supplies; two officers (one from Stately , one from Thames ) step ashore for a duel by guns, each fatally wounded, not resolving the bad feeling over the Stately' s fighting qualities. They reach Freetown again, now in the dry season, meeting the British colonial governor and his wife, herself an esteemed naturalist, happy to meet Maturin. Maturin leaves the potto he had aboard in her care.
Aubrey hastens to meet the French squadron, commanded by the wily Commodore Esprit-Tranquille Maistral, south and east of the point the French are expected to meet the Caesar arriving from America. Caesar fails to arrive, so they proceed northeast to Ireland. Aubrey informs his captains of his plan of attack and the Bellona attacks the French pennant-ship, with the Thames and Stately attacking the other French two-decker ship. The first strikes on a rocky shelf and surrenders; the second badly mauls the Stately and flees eastwards. Thames is stuck in a reef. The four French troop carriers and one frigate, which are penned in a cove, are handled by HMS Royal Oak and Warwick , who join the scene of battle, having heard the gunfire. The other French frigate slips away. Bellona is taking water and Aubrey is glad for the help. Ashore, Maturin speaks to the Irishmen who so badly want the guns aboard the foundered ship. He and Father Boyle persuade them this is not the moment, as anyone found with the French guns by the British will be hanged. After tending the wounded, Maturin learns from his friend Roche that the flags are at half-staff on account of the death of a minor royal, the Duke of Habachtsthal. He has committed suicide. Maturin, pleased at the news, proceeds to the home of Colonel Villiers, a relative of Diana's late husband with whom she is now living, where he and Diana are happily reunited.