Among a batch of cultural relics, there is a diary in urgent need of restoration. The sincere and kind young restorer Liu Yuan takes over the task, and her partner is Wang Ze, a suave restoration expert who has returned from studying abroad. The two people with different positions inevitably had some "friendly" exchanges at work, but as the restoration work progressed, the two also uncovered a dusty past: in the 1930s and 1940s, the female agent Zhao Deng Man was ordered to sneak into a hotel and perform a mission with a man code-named "Fox". A sudden accident trapped everyone in the hotel for investigation. Many forces were involved. It was full of mystery about who was the enemy and who was the friend… What other secrets are waiting to be revealed?