In 1935, Tianjin Wei was surrounded by Chinese and foreign affairs, and undercurrents were surging. Under the guise of commerce, Japan's "Kanto Colonization Society" coveted the legendary "Bohai Dragon Box" that contained the secret weapon and navigational charts of Zhenhai. It attempted to control the shipping in the Bohai Sea and plunder the resources of North China.
The nine major families, the "Nine Guards of Jinmen", once made an alliance to guard the Dragon Box, but were later separated due to differences, and now they are forced to regroup. The captain of the detective team, Shen Yan, dealt with various forces in order to find out the truth about his father's mysterious death and the whereabouts of the Dragon Box; the leader of the "Jinghong Squad", Lu Jinghong, bore the blood feud of his deceased wife, and used his exquisite voice control technology to help protect the treasure; the ancient book restorer Su Qingyuan returned with the fragmentary picture of the Dragon Box left by his father, and became the key to deciphering it with his unique skills.
There are also Qi Mo who is good at feng shui divination, Huo Linglong who is in charge of water transportation, and Xie Mingyuan who is skilled in mechanical codes... From being suspicious of each other to fighting side by side, the Nine Guards must not only crack the numerous mechanisms of the undersea tomb, fight against the machinations of Japanese spies, but also deal with the greedy calculations of warlords.
In the shadow of the sword, there is the persistence of the righteousness of family and country, the bond of life and death, and the deep love between Shen Yan and Su Qingyuan that grew up in the crisis. They used the power of the Nine Guards to build the Jinmen barrier, and in the wars of troubled times, they composed a legend about protection, faith and passion.
