The water level in Hanting Town rises sharply, and the long-sealed old case of the breached tidal gate stirs up waves once again. Carrying his father's grievance, a young blade master brings half a gate pin to investigate the truth, moving from mutual suspicion to walking shoulder to shoulder with a ferry girl familiar with the waterways. Along the way, they join hands with a blacksmith, a gate-keeping apprentice, and an old gate-keeper, following clues such as broken cable piles and missing gate pins to gradually uncover a conspiracy where someone intentionally sabotaged the water gate to cover up the old case. Facing the approaching flood and heavy obstacles, everyone puts the safety of the common people first, joining forces to reclaim the gate pin, repair the mechanism, and stabilize the water level. At break of dawn, the crisis is resolved, and the truth of the old case gradually becomes clear.