In the 1950s, overseas student Ji Danyang returned to China and devoted himself to national defense research. After arriving in Hong Kong, he fell into the trap of enemy spies. Public security officer Pang Hongmei protected Ji Danyang and returned to the motherland safely, but after the enemy spies failed in Hong Kong, they continued to deploy the "Rock Plan" around our "Water Drop Project" in Lumen, hosted by the spy "Snow Wolf", trying to sabotage our scientific research tasks. In order to ensure the smooth development of the Water Drop Project, public security personnel represented by Pang Hongmei and enemy spies launched several confrontations, but at each key node of scientific research, the enemy spies were always able to deploy sabotage plans one step ahead, and the Snow Wolf had not been found. The enemy spies were still secretly sabotaging the "Water Drop Project". Pang Hongmei and other public security officers had a life-and-death battle with the enemy spies in Lumen... In the process of protecting the expert group, Pang Hongmei, Ji Danyang, and Bai Hui, a nurse at the factory hospital, gradually got to know each other and became friends. When Pang Hongmei began to doubt the identity of Bai Hui's father, Bai Minghan, a traditional Chinese medicine practitioner, where should their friendship go?