The Hundred Days by Patrick O'Brian

Set during Napoleon’s sudden return from exile in 1815, the novel follows a seasoned Royal Navy captain and his friend, a surgeon-cum-spy, as they resume a blend of sharp sea tactics, intelligence work and shipboard life; pursuing French privateers, negotiating delicate diplomacy and supply issues, and managing strained personal relationships, they must confront how the swift political upheaval ashore—culminating in the decisive land battles—reverberates through their commands, careers and friendships at sea.

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