Wen Zhiyu is sent by her family to a castle for a marriage alliance. She expects an uncertain future, but unexpectedly meets Ye Jin, the Night Lord she has secretly loved for ten years. Though she appears delicate and timid, she is actually clever and clear-minded. Drawing on years of research, she helps him uncover an old misunderstanding and resolve the castle's troubles. The cold and lonely Ye Jin gradually opens his heart through her companionship. From misunderstandings and cautious testing to standing side by side to protect one another, the two ultimately bring long-awaited light back to the castle.