In ancient China during the Tang Dynasty, a powerful and mysterious sea monster disrupts a wedding ceremony on a royal ship, causing widespread panic. The dragon-like creature's attack prompts the emperor to task Yuchi Zhenjin, head of the Divine Constabulary, with solving the mystery. Meanwhile, a young and talented Dee Renjie arrives in the capital with aspirations of serving justice. With his sharp intellect and keen observation skills, Dee becomes embroiled in the investigation. He faces resistance from Yuchi, who is initially skeptical of Dee’s abilities. However, when Dee's insights prove invaluable, he is reluctantly accepted into the team.

As they delve deeper into the case, Dee and Yuchi discover that the sea monster is connected to a larger conspiracy involving dark forces and corrupt officials. They encounter a series of clues leading them through perilous encounters and hidden secrets. The duo must use their combined wits and bravery to unravel the truth, facing dangerous adversaries along the way. Their pursuit unveils a tangled web of intrigue where the line between allies and enemies blurs. The young detective’s journey is a test of wisdom, courage, and the relentless quest for justice amid mounting threats.