The Invisible Castle. Luong Doi practices with his students the mental powers that can be used to move objects. A stone falls on his head, he becomes a little more confused than usual and keeps fainting. Junxiu, Cheng's sister, discovers a lock that suddenly disappears. Cheng, Tang and Hua take Luong Doi to Cheng's village for treatment for his injury, but the village has burned down and all the residents have disappeared. Luong Doi concludes from the pieces of armor that the black foxes are not behind it, but the soldiers of Gentai, who had placed a curse on his castle so that it would become invisible to his enemies. From time to time this castle reappears and Gentai captures the villagers in order to terrorize and imprison them. Luong Doi leads our friends to the castle, they manage to break through the wall and free the prisoners including Cheng's parents and Cheng's sister Junxiu.