Jack Aubrey's long service is at last rewarded: he is promoted to the rank of commodore and given a squadron of ships to command. His mission is twofold, to make a large dent in the slave trade off the coast of Africa and, on his return, to intercept a French fleet set for Bantry Bay with a cargo of weapons for the disaffected among the Irish. This is the 17th Aubrey and Maturin novel.