In early October 1813, following a shocking mutiny and the pirating of HMS Expedition at sea, Captain Fly Austen of HMS Invincible is determined to go after the person responsible, the English traitor Thomas Trevelyan, but is waylaid by a calamitous storm. Arriving in Halifax, Nova Scotia, to refit and recover, he soon hears rumours of Trevelyan’s whereabouts, and is fortuitously ordered to Boston to negotiate the release of British prisoners of war.
After insisting his reluctant friend, Dr. Leander Braden, accompany him, they set off on an American sloop, taking Magpie and Prosper with them, unaware that Princess Emeline “Emily” Louisa and an old adversary are also on board. In Boston, Emily falls into the wrong hands, and Leander and Magpie must find a way to board the ship on which she is being held. An attempt to recapture Trevelyan and retake the Expedition ends in a final battle and tragedy.
Meanwhile, those left behind in Halifax, including Gus Walby, Biscuit, Eliza Braden and Fleda Lindsay, endure the grim realities and lessons of life while appreciating unexpected opportunities for new beginnings.