Beidousi is a mysterious organization under the Imperial City Division in the Northern Song Dynasty. All its members are codenamed after the stars of the Big Dipper. They each have different powers and master the magical and advanced technology at that time. They are the personal guards who directly obey the emperor's orders, and they are also a barrier to protect the court and the people of the world. Tai Sui, a reckless teenager with an "immortal body", accidentally met Wu Yaoguang, a violent loli with superpowers, and Liu Suifeng, a romantic wanderer, and followed them to join Beidousi. After that, they repeatedly solved strange cases and punished evil and promoted good. Through a series of cases, Tai Sui gradually discovered that his "immortal body" was related to his confusing life experience, and there was a bigger conspiracy behind these cases. He was unwilling to go along with the evil forces, and used loyalty, friendship and wisdom to unite his partners and continue to grow. Finally, with the help of righteous people, they finally found and punished the original culprit, upheld justice, and benefited the people. Tai Sui also finally found his lost family and harvested a beautiful love.