Havoc's Sword by Dewey Lambdin

It's 1798, and Lewrie and his crew of the Proteus frigate have their work cut out for them. First, he has rashly vowed to uphold a friend's honour in a duel to the death. Second, he faces the horridly unwelcome arrival of HM Government's Foreign Office agents (out to use him as their cat's-paw in impossibly vaunting schemes against the French). And last, he must engineer the showdown with his arch foe and nemesis, the hideous ogre of the French Revolution's Terror, that clever fiend Guillaume Choundas!