S1·E33 Dong Yi Discovers The Cause of the Plague

Jang Ok Jeong finds out that it is her mother who causes the plague. She however ignores it because of her hate towards Dong Yi. In the meantime, Southern Faction finds no early records about Dong Yi and Cheon Soo. So, they try to get the information from Dong Yi's friends. Dong Yi meanwhile discovers that the plague is caused by the poison in the cosmetics that are linked to Jang Ok Jeong's mother. But, she is arrested because her three days limit is over. The King has been informed about the investigation and when he goes to question Jang Ok Jeong, she says that she and her mother know nothing about it. Then, delegates from Qing are coming to acknowledge the Crown Prince.