Guo Zilu is in the middle of drinking when Cao Xuanxuan arrives with He Chuner to see him. Because he dislikes Cao Xuanxuan, Guo Zilu greets her with a cold demeanor. However, Cao Xuanxuan pays no mind to his attitude and sends He Chuner and Guo Zilu’s servants away so she can discuss with Guo Zilu how to pursue new leads. Guo Zilu claims he has already caught the person who was cursing his father that day. Naturally, Cao Xuanxuan doesn’t believe a mere curse could kill someone, but Guo Zilu stands his ground. Seeing that Guo Zilu clearly has no desire to discover the real culprit, Cao Xuanxuan decides to investigate on her own. She steps outside, intending to take He Chuner to the woodshed to see the girl named Ruohui, the one allegedly performing the curse—only to find Ruohui has already run away.
He Chuner examines Master Guo’s body and finds his only fatal wound is on his waist, inflicted by a dagger. Cao Xuanxuan is suspicious. The second madam died from poison, while Master Guo died from a stab wound; the different causes of death make the case all the more confusing. Cao Xuanxuan decides to inspect Master Guo’s room for clues and summons Sun Weiyan as well. She suspects Master Guo’s case might follow the same pattern as the others—another so-called “locked-room murder,” in essence an assassination.
Elsewhere, Dujuan and Zhang Yuan meet in secret at a designated spot. Dujuan urges Zhang Yuan to leave quickly, fearing Cao Xuanxuan’s investigation might expose them. Zhang Yuan reassures Dujuan that nothing will happen. After sending Dujuan away, he goes straight to Cao Xuanxuan, attempting to take all the blame upon himself. But the many reasons he gives fail to convince anyone—nor can he explain the source of the poison. Cao Xuanxuan realizes Zhang Yuan is covering for someone but finds him unwilling to talk.
Cao Xuanxuan then asks the steward which people in the household might have held a grudge against the second madam. The steward reveals that Dujuan and Guo Zilu once exchanged harsh words in front of the second madam and thus bore a grudge against her. Cao Xuanxuan concludes that Zhang Yuan must be taking the fall for Dujuan. Not wanting to alert their suspects, she advises the steward not to tip them off. Due to the second madam’s death, Dujuan has been extremely on edge. She frantically goes looking for Guo Zilu but happens to be spotted by Cao Xuanxuan, who also discovers the poison in Dujuan’s room. Realizing his involvement has been exposed, Guo Zilu immediately denies any responsibility and leaves the scene. Dujuan, however, insists that Zhang Yuan has nothing to do with the case and that she never poisoned the second madam. She claims she did ask Zhang Yuan to buy poison, but never actually used it, and has no idea how the second madam ended up poisoned. At that moment, Guo Zilu suddenly enters; refusing to let Dujuan explain further, he orders her thrown into prison to be executed.
Sensing there is more to the story, Cao Xuanxuan doesn’t rush to settle the matter. She merely has Dujuan detained and then takes the poison to a pharmacy for inquiry. The shop owner informs her that the poison Dujuan bought has never been used.
Meanwhile, while Ruohui is eating, she hears that Master Guo really is dead. Believing it must be the result of the “magic” taught to her by Zhang Daxian, she rushes off to find him. Since two people in the Guo family have died in quick succession, Ruohui fears she “killed the wrong targets.” Seizing on her fear, Zhang Daxian demands hush money from her. Sun Weiyan and He Chuner track Ruohui down and bring her back to the Guo Residence, also obtaining the poison Cao Xuanxuan seeks.
Based on her analysis of that night’s events, Cao Xuanxuan concludes how the second madam really died. The poison had been placed in the well. Because of its high density, it settled at the bottom. As the hostess, the second madam’s cup would have been filled last from the pitcher of water mixed with wine—thus she was the one who ingested the poison. In the end, Dujuan and Zhang Yuan are both expelled from the Guo Residence.
After Ruohui is brought before Cao Xuanxuan, she finally reveals her true hatred for Master Guo. Years ago, Master Guo and Ruohui’s father were friends who encountered bandits together. Ruohui’s father, whose leg was injured, gave Master Guo and the steward a chance to escape. No matter how it might be explained, Ruohui still blames Master Guo for her father’s death. Learning about the so-called “spiritual mentor” Zhang Daxian behind Ruohui, Cao Xuanxuan suspects there is more to Master Guo’s connection with him. Using a strategy of “releasing one to catch the bigger fish,” she deliberately lets Ruohui go, giving her a large sum of money in hopes of uncovering the truth behind Zhang Daxian’s involvement.
