Former Brocade Guard Commander-in-Chief Li Wu lives hidden in the countryside, while his son Li Chang'an is determined to take the Brocade Guard exams. Court officials spontaneously combust mysteriously, the Red Lotus Cult stirs up trouble in secret, and the emperor three times invites Li Wu to come out of retirement. Father and son join hands, uniting with young colleagues to crack the red phosphorus murder mystery, smash the conspiracy between the cult and the Ministry of War, with the youth growing all along the way, combining humor and the satisfying thrill of solving cases.