In the wildly popular British series “Poldark,” Ross Poldark returns to Cornwall after the American War of Independence to find his estate in ruins, his finances exhausted, and his first love engaged to his cousin. Determined to rebuild, he reopens his copper mines, marries his former kitchen servant, and champions the working class, even risking his life in a duel. Historian Julie Taddeo examines the show’s topics—economics, religion, marriage, medicine, social customs, fashions, and the details of daily life in Cornwall and London—and explores what the series portrays accurately about the period and what its creators fictionalized.