As a quiet, book-loving noblewoman, she was always unfavorably compared to her flashy twin sister and shunned by her family. Her miserable life takes a terrifying turn when her sister seduces an engaged prince and is punished with an order to marry the rumored "Reaper Duke"—a terrifying man whose wives always die mysteriously. To protect his favorite child, their cruel father forces her to take her sister's place as a substitute bride. With no way to escape, she prepares for her doom and marries the duke. However, to her utter surprise, her new husband is a perfect gentleman who continuously saves her from danger! Why is such a genuinely kind man known as the Reaper Duke? What begins as a deadly sacrifice slowly blossoms into a sweet and mysterious romance!