Treason's Harbour by Patrick O'Brian

Another re-read. This is one of the books that gets deepest into Maturin's work as a secret agent, and this gives it overall a very tense story (especially as we the readers know of a traitor that he does not). It is also the first time we really get to know Reverend Martin, and his unfortunate habit of being bitten, stung or otherwise abused by random creatures.