Lu Xiao is the captain of Haigang Police, who is wise and calm. Despite his young age, Lu Xiao is seen as an elite member of the police force, as he has solved multiple complex cases. However, a bizarre case of a floating corpse and a killer nicknamed the "Water Ghost" stumps Lu Xiao. During the investigation, the killer escaped multiple times, but with his new roommate Fang Yi Tong, the two team up to catch the killer.