The Commodore — Patrick O'Brian

Having survived their adventure in the Great South Sea, Captain Jack Aubrey and Stephen Maturin now return to England. For Jack it is a happy homecoming, but for Stephen disastrous: his little daughter appears to be autistic, incapable of speech or contact, and his wife, Diana, has disappeared.

Aubrey and Maturin are sent first to the Gulf of Guinea to suppress the slave trade, but their ultimate destination is Ireland. There the French are mounting an invasion that will test Aubrey's seamanship and Maturin's resourcefulness as a secret4ntelligence agent, and the climax of the story is one of those grand fleet actions on which the supremacy of the British Navy was founded.