Duke Xue arrives at the coming-of-age ceremony with an imperial edict to arrest Yan Lin and his father due to their army's rebellion. He’s been working with King Ping Nan to insert rebels into the Yan family’s army so they can instigate a rebellion and implicate the Yan family. Zhang Zhe stops the arrest on a technicality, which Duke Xue eventually overcomes. He also confronts Xie Wei on his incomplete ceremonial speech to Yan Lin. (Source: frankly at MyDramaList)