H.M.S. Surprise (Aubrey-Maturin series, Book 3)

Ashore without a command--and on half-pay to boot--Jack Aubrey's prayers are answered when Stephen Maturin shows up with a secret mission for him. The two men have been ordered to the Cape of Good Hope. There they hope to dislodge the French garrisons on the islands of Mauritius and La Reunion. Alas, two of their own colleagues--a dilettante and a martinet--prove to be nearly as great an obstacle as the French themselves.