When Song Yimeng heard something happened to Nan Heng, he was anxious to search for evidence.She found out the letter Chu Guihong had written to her, which proved that Nan Heng was in a difficult situation at the time and could not collude with foreign enemies.During the trial, Chu Guihong provided evidence that Nan Heng ordered people to assassinate Lu Yi. Nan Heng refuted the forged testimony, saying that A Long and A Hu who were sentenced to death were sent to the clinic and could be summoned to confront each other at any time.

Nan Heng also questioned that the secret of the Qianyu Army's defense was leaked in the Battle of Pingrong, and suspected that the commander behind the scenes was manipulated, and both sides had their own opinions.At this time, Song Yimeng beat the drum and made a fuss. He rushed into the yamen with the people and took out the letter, but Chu Guihong accused Nan Heng of having accused him of having been in the forbidden city, and had treasoned him for treason and colluding with the enemy as early as the forbidden city.Yao Qian suddenly appeared in the Ministry of Justice and took out the so-called letters from Nan Heng colluded with Heyuan people whom he had found in the study of the prince's mansion.After reading the rumor among the officials, Chu Guihong asked to take Nan Heng.
At this time, Eunuch Liu came with an imperial edict, saying that Nan Heng colluded with Heyuan and treasoned the country, and detained him in prison.Song Yimeng could not stop him. Nan Heng asked Shangguan He to protect Song Yimeng Zhou Quan and went to prison with the guards, and told Song Yimeng that as long as she believed in her, she would be innocent.Song Yimeng blamed himself for helping him, and listed Nan Heng's past achievements on the paper. Outside the gate of the palace, he knelt in the snow, holding a paper with Nan Heng's achievements pleaded with mercy.