Cheng Feng returns to the capital as a prisoner and accuses General Cui Yi of colluding with Jieshuo. Though Li Ni knows this is a lie, the Emperor and his ministers are easily convinced and call for General Cui Yi to return to the palace to face his crimes. Li Ni convinces General Cui Yi to return with him to the capital so they can prove his innocence but the investigation goes nowhere. (Source: frankly at MyDramaList)