When a young man and woman vanish, Zhao Yunlan and the SID team are called to investigate. Shen Wei can't seem to stay away from the case either, and Zhao Yunlan continues to try and discover what Professor Shen is hiding from him.
The episode opens with a fancy car pulling up to a mansion. A young man named Huang Linqi gets out and goes inside where he is greeted by the butler, Wu Tian’en. Butler Wu greets Huang Linqi, calling him “young boss,” but Huang Linqi gets angry, saying that Butler Wu should just call him “boss.” Huang Linqi’s father, Huang Chaoyang, appears and exchanges angry words with his son. Huang Linqi storms off and goes to take a bath. But when he’s in the bathtub, something strange starts happening with the water running out of the tap. Huang Linqi suddenly screams as something pulls him into the water, and then he disappears.
The next scene is at Dragon City University. Shen Wei is having tea with the Chancellor. The Chancellor says that rumors have been circulating about Shen Wei because he has been involved in the recent murder cases and seems to always be around the SID investigators. The Chancellor suggests that it might be a good idea for Shen Wei to move out of the faculty dormitory for now. Shen Wei says that he has already found an alternative residence.
We cut to the SID where Lin Jing has made popcorn in one of his scientific devices. In his eagerness to get some popcorn, Zhao Yunlan jumps right up onto the table. Zhao Yunlan asks if they have any new cases, and Zhu Hong hands him a folder. Their next case involves Huang Linqi’s disappearance.
At the mansion, Lin Jing collects evidence in the bathroom while Zhao Yunlan, Chu Shuzhi, and Guo Changcheng speak to Butler Wu and Huang Chaoyang. Huang Chaoyang doesn’t know the correct name of the SID, and Chu Shuzhi starts to correct him, but Zhao Yunlan stops him from being too impolitic. Huang Chaoyang brushes them off and says Butler Wu will answer their questions. He goes to speak to another man, who Butler Wu reveals is the father of the girl that Huang Linqi is supposed to marry. Her name is Li Jiaqi.
We leave the SID team for a moment and return to Shen Wei, who is walking through an apartment with a realtor. The realtor suggests that Shen Wei might find another location more appealing. Shen Wei looks at the door across the hallway, smiles, and says “I’ll take this one.”
Meanwhile, Li Jiaqi is at home with her father. Her father says that because Huang Linqi has disappeared, they should look for a different husband for her. Li Jiaqi ignores him and goes into the bathroom, where she starts filling the tub. Suddenly, she gets pulled into the water too, just like Huang Linqi.
The SID comes to investigate, and Zhao Yunlan discovers writing in the steam on the mirror. Meanwhile, Butler Wu goes to a nearby lake and starts talking to the water. He is followed by Lin Jing and Chu Shuzhi, who then bring Butler Wu in for questioning thanks to this suspicious behavior. Lin Jing also takes a sample of the lake water. Zhao Yunlan interrogates Butler Wu at a café and Butler Wu reveals that he has been the butler for Huang Chaoyang for twenty years and seven months. Zhao Yunlan asks him if he’s ever heard of Dixingren. Butler Wu says no, but glances at someone walking by in the street. Zhao Yunlan sees the person too and realizes it is Shen Wei.
Zhao Yunlan lets Butler Wu go, but as Butler Wu is walking away, Shen Wei confronts him. Frightened, Butler Wu reveals that he has a teleportation power and is really a Dixingren. Shen Wei then reveals that he is the Black-Cloaked Envoyi, and Butler Wu falls to his knees. He knew the Black-Cloaked Envoy from Dixing. Shen Wei notes that Butler Wu cannot move as quickly as he once did and also that Butler Wu has a cough—he asks what is wrong with Butler Wu’s body, but Butler Wu says that it is nothing. Shen Wei lets it go and tells Butler Wu that he will not interfere with the SID investigation, but that whatever Butler Wu plans, he better not touch Zhao Yunlan. As Shen Wei walks away, he is thinking about Butler Wu’s poor health and diminished powers and says to himself, “Then how much more time is left for me?”
Meanwhile, the SID team is brainstorming about the case. Da Qing suggests calling the Black-Cloaked Envoy, but Zhao Yunlan immediately says no. Then Lin Jing discovers that the water he collected from the crime scenes does not come from the city pipes, but rather matches the water he collected at the lake. Chu Shuzhi wants to rush off and arrest Butler Wu, but Zhao Yunlan says they don’t have enough evidence yet.
Later, Zhao Yunlan calls Shen Wei at his office. He tells Shen Wei that he saw him walking by the café earlier. Shen Wei artfully avoids revealing any information, and Zhao Yunlan laughs and says he’s lucky Shen Wei isn’t a criminal suspect, as he isn’t sure which one of them would win. But he adds that if Shen Wei is hiding something, he’ll be sure to find out the truth eventually. Shen Wei says that he’ll do anything he can to help Zhao Yunlan and the SID, and Zhao Yunlan says that he does indeed have some questions for Professor Shen.
Back at the mansion, Butler Wu is leaving with a suitcase. Huang Chaoyang stops him. Butler Wu says that his son, Wu Xiaojun, has returned, and he must go find him. Huang Chaoyang is disturbed and asks Butler Wu how he can be sure. Butler Wu admits he hasn’t actually seen Xiaojun, but he knows where he can find him.
Next, we see a flashback. Butler Wu has just returned from a trip, and Huang Chaoyang tells him that Xiaojun is missing. Huang Chaoyang says that he is helping search, and that he views Butler Wu as his brother, and Xiaojun like his own son. We return to the present where Butler Wu is sitting by the lake. Chu Shuzhi and Guo Changcheng are spying on him. A figure, composed of water, emerges from the lake. Guo Changcheng is impressed because Zhao Yunlan had figured out that the culprit could travel through the water. Chu Shuzhi grumbles that there is no need to flatter Zhao Yunlan because he isn’t there.
Butler Wu is elated because this is his son. But Xiaojun is upset—he says that his father wished he was dead because he thinks Xiaojun is a monster. He says that Huang Chaoyang took him to the deserted mountains and abandoned him there—he didn’t run away. He kept waiting for his father to find him, but he never did.
Meanwhile, Huang Chaoyang is calling Li Jiaqi’s father. He tells him that Butler Wu is going to find out what really happened. Li Jiaqi’s father sent two men to tail Butler Wu. Huang Chaoyang says that when the opportunity presents itself, he should have them kill Butler Wu and Xiaojun. We see a flashback to Xiaojun manipulating water as a child, and Huang Chaoyang and Li Jiaqi’s father seeing him and calling him a monster.
Back in the present at the lake, Butler Wu doesn’t want to believe that Huang Chaoyang lied to him. He sees that Xiaojun is still wearing a ring that he gave him. Xiaojun appears to throw the ring away in a rage. Butler Wu says that his son can hate him, but that Huang Linqi and Li Jiaqi are innocent and Xiaojun must let them go. Xiaojun is furious and demands how his father, who he still feels abandoned him, can beg him for the lives of other children. Xiaojun disappears back into the lake.
In another part of the lake, Huang Linqi and Li Jiaqi are bound together with ropes of water. As they try to get free, they realize that they actually want to marry one another. Xiaojun appears and mocks them, then begins to drown them. Butler Wu uses his teleportation power to follow his son, and he stops him. He falls to his knees and begs his son to blame him, but not the other children. Xiaojun wavers and then relents and releases Huang Linqi and Li Jiaqi. He hugs his father, crying. But then the two men Li Jiaqi’s father sent to tail Butler Wu appear, and one of them shoots Butler Wu with a poisoned dart. Chu Shuzhi and Guo Changcheng come running up, but Xiaojun escapes into the water again.
We cut to Huang Chaoyang relaxing by his swimming pool. He is castigating Li Jiaqi’s father over the phone for failing to kill Xiaojun. The water in the swimming pool starts to bubble and then Xiaojun appears. Huang Chaoyang is ready, though, and electrocutes him. He has his bodyguard beat Xiaojun and forces Xiaojun to open his hand. Xiaojun has been clutching the ring that his father gave him. Huang Chaoyang takes the ring and calls it worthless. Furious, Xiaojun overpowers the bodyguard and starts to kill Huang Chaoyang. But Zhao Yunlan comes out of the house, interrupting him and stopping him. Zhao Yunlan tells him that Huang Chaoyang will be punished and that Xiaojun should really be concerned with his father.
At the SID, Butler Wu is lying on the couch, dying. Xiaojun begs Zhao Yunlan to save him. Distressed, Guo Changcheng runs and gets the Longevity Dial. He asks Zhao Yunlan for permission to use it to save Butler Wu. But Zhao Yunlan grabs the Dial himself. He tries to activate it—at first nothing happens, and Lin Jing wonders why the Dial sometimes works and sometimes doesn’t. Desperate, Zhao Yunlan tries again and this time it begins to activate. But at that moment, the Black-Cloaked Envoy appears. He demands to know what Zhao Yunlan is doing, activating a relic. He asks if it is worth it to Zhao Yunlan, to shorten his own life to save a Dixingren.
We cut to Zhu Jiu at his game board. He says that the father and son are useless and that it is time to initiate the second step in the plan instead.
Next, we go to Dixing where Butler Wu and his son are walking with the Black-Cloaked Envoy. Two soldiers appear and demand that the Black-Cloaked Envoy hand them over. They claim they have an order from the king. Shen Wei steps to the side, but as the two soldiers level their guns at Butler Wu and Xiaojun, Shen Wei vanishes the soldiers. Butler Wu and Xiaojun are alarmed at this evidence of conflict and potential treachery in Dixing. Shen Wei begins to question Butler Wu. He says that Butler Wu was part of a team that had been dispatched to Haixing to try and find the relics. Shen Wei lost contact with the team, and he asks Butler Wu what happened.
Butler Wu says that the team was in a forest when they were surrounded by ghost-beasts (youchu). He was knocked unconscious, and when he awoke, everyone else was dead. Shen Wei reveals that the captain survived and hid in Haixing, committing crimes. Before Shen Wei could capture him, he was shot dead. Butler Wu remembers the captain telling him before they left on the mission that his wife had recently become pregnant, and so he might have a descendant who might know more about what happened.
Meanwhile, at the SID, Zhao Yunlan is looking at the Longevity Dial. He remembers the Black-Cloaked Envoy saying that the Dial should not be activated again. Suddenly, the Dial lights up and projects an image of the Mount River Awl.
At the end of the episode, we begin the next case that SID will need to solve. An unfamiliar man and woman are lying together in bed, and there are pictures of them together up on the walls. The woman’s name is Zhou Weiwei; the man is Ji Xiaobai. Weiwei gets up and goes into the bathroom, turns on the shower, and looks into the mirror. A little while later, Xiaobai goes to see what’s happened because she hasn’t come back to bed. But there is no one in the bathroom.
In the next scene, Da Qing and Zhao Yunlan are out jogging. Da Qing is complaining, and Zhao Yunlan tells him that he needs to be in shape and ready for anything; he should think of Professor Shen and how Shen Wei is always so good at helping them out. As they reach Zhao Yunlan’s apartment building, they run into Shen Wei. Zhao Yunlan is surprised and asks him what he’s doing there. Shen Wei tells him that he just moved there. After Shen Wei leaves, Zhao Yunlan says to Da Qing that Shen Wei deliberately didn’t tell them his exact address, and Da Qing thinks smugly that it isn’t that difficult to find out such information.
The next scene is of Guo Changcheng who is trying (badly) to tail Chu Shuzhi. But he loses sight of him and Chu Shuzhi comes back around behind him, berating Guo Changcheng. Zhao Yunlan pops up too and tells Changcheng that he has failed this test seven times. Before poor Changcheng can reply, Zhao Yunlan’s phone rings—they’ve been called in on the case of the missing girl.
At Xiaobei and Weiwei’s apartment, Zhao Yunlan examines himself in the mirror in the bathroom while Guo Changcheng and Chu Shuzhi look for clues. They have an electronic bug, one of Lin Jing’s creations, that can tell that there are no signs of blood and that there are no footprints or fingerprints besides Weiwei’s and Xiaobei’s. Changcheng wonders if maybe Xiaojun is back again, but Zhao Yunlan says that he was taken by the Black-Cloaked Envoy and no one ever comes back from that. Zhao Yunlan reveals that there is a steward in Dixing also, and when Changcheng is surprised that Dixing has more officials than the Black-Cloaked Envoy, Chu Shuzhi becomes quite philosophical and says that people always form hierarchies and that this will always lead to killing and oppression.
Zhao Yunlan goes and questions Xiaobei again. Xiaobei reveals that this isn’t the first time something strange has happened. We see a flashback of Weiwei being choked by a woman whose face we can’t see. Xiaobei rushes in and separates them. He asks Weiwei if she is all right, and then when he turns around, the other woman has vanished.
Shen Wei moves in across the hall.
Da Qing: "I, the honored ruler of the cat world, am actually going so far as to accompany you on a morning run."
Lin Jing: "Science is a rite of passage in our continuing evolution, but if you know there's a wall in front of you, why throw yourself at it?"