Mi-jin leans in to kiss Ji-ung, but he misunderstands, thinking she’s going to headbutt him like before, and blocks her advances. Embarrassed, she rushes out. Da Yeong is busy gushing over kissing couples on the screen and notices Mi Jin’s behavior. That’s when Mi jin tells her about Ji ung’s rejection. Dayeon is embarassed for her friend. Later that night, Mi-jin and Da-yeong awkwardly come across Ji-ung in the convenience store where she mistakenly flings a can of beer at him without realizing his presence. Mi-jin apologizes to him and leaves without hearing him out.
While in his apartment, Ji-ung is bothered by Mi jin when he suddenly comes across the autopsy report of director Baek Chul-kyu’s wife, where fentanyl was found in her blood. However, Baek Chul-kyu was not found guilty. He revisits the geographical sites of the murders on the map and recalls that the severed foot also had traces of fentanyl in the blood of the victim. Ji-ung concludes that the recent murder might have been an accident, which is why the culprit might have disposed of the body nearby. He then deduces that there is a high chance of the body being found in the nearby reservoir.
The next day, Lim Sun is visibly irritated with Ji-ung, while Joo Byung-duk is shocked to see Lim Sun and Ko Won suspiciously close to each other, hilariously misunderstanding that they might be in a relationship. Later, while Ko Won is in the office, he receives an anonymous letter stating that one of the senior interns is lying about their identity. Assuming the letter is about Lim Sun, he disposes of it.
Meanwhile, Ji-ung asks the police to search for the victim in the reservoir again. He is scolded by the chief for digging too deep into the case. Lim sun witnesses this and feels sorry for him. However, the police had previously searched the reservoir, but since it was too deep, they called off the operation without finding anything. Later that day, while waiting for Da-yeong to join her at a popular restaurant, Mi-jin meets Ji-ung and Byung-duk. The four awkwardly share drinks. Do yeon mistakenly throws away snacks leaving Ji ung and Mi jin to pick it up together. Byung Duk then tries hitting on Do Yeon but she indirectly rejects him and says that her type is Ko won.
The topic arises that nobody can resist Ko Won, and they ask Mi-jin what she’d do if Ko Won asked her out. Ji ung gets jealous and uncomfortable with the question but Mi jin indirectly answers that she likes Ji-ung, later confirming this in the cab on the way home while everyone is drunk. Ji ung wants to say something to her but stops himself when they get to his house. After dropping off a drunk Do yeon, he leaves unable to tell her his mind.
In the next few days, a decayed body is found floating in the reservoir, which turns out to be the victim, Ko Na-heun. When Ji ung sees his grieving daughter, he is reminded of the time when his mother had gone missing and her body was never found. The young Ji-ung would sit in the police station, but the police couldn’t find his mother. Meanwhile, news spreads about the police’s incompetence due to their inability to find the body for over a month. Byung Duk’s suspicion of Lim Sun and Ko won’s relationship heightens when Lim sun rejects his dinner invitation only to find her meeting Ko won outside the office. He is in disbelief when he sees him dropping her off in his car. Elsewhere, Baek Chul-kyu contacts the head of forensics, possibly to alter the autopsy report of the victim.
The news about Ko Na-heun also reaches Lim Sun, who briefly chases after Baek Chul-kyu and notes his car number. She realizes that his car number was on the list of suspects for the murder and frantically conveys this to Byung-duk, but he and Ji-ung are already aware. They don’t have enough evidence to arrest Baek Chul-kyu.
At forensics, the doctor tells Ji-ung that the victim died of drowning rather than any unnatural events. They also found traces of fentanyl in his blood but in a moderated amount, which further implicates Baek Chul-kyu, as he’s a medical professional. Meanwhile, Ji-ung’s search and seizure request for Hwadong Medical Centre is rejected by the higher-ups.
Ji-ung and the team then decide to take matters into their own hands. Lim Sun pretends to be a patient while Ji-ung and Byung-duk gather evidence against Baek Chul-kyu. Meanwhile, Baek Chul-kyu learns about Lim Sun’s presence in the hospital and rushes to her while they take her blood for a blood test.
In the meantime, Lim Sun escapes and makes her way to Baek Chul-kyu’s office to gather evidence, with Baek Chul-kyu hot on her heels. When Baek Chul-kyu enters his office, Lim Sun hides in one of the closets. Just when she’s about to be discovered, Baek Chul-kyu receives Lim Sun’s blood test results. However, when he compares her current blood test to one from 20 years ago, he finds they’re different and wonders who Lim Sun really is.
IN episode 10, the trio—Ji-ung, Mi-jin, and Byung-duk—gather evidence against Baek Chul-kyu at Hwadong Medical Centre.
While Ji-ung finds an odd-looking medicine in the basement storage, which is to be sent for analysis, Byung-duk discovers a large stock of fentanyl in the pharmacy. Meanwhile, Lim Sun manages to get hold of Baek’s shaving razor for a drug test. The three barely escape from the medical centre, with Lim Sun wondering why Baek has her aunt’s blood test from so many years ago.
The next day, Lim Sun finds that Baek has taken leave for a few days and is secretly worried about her safety should he discover what she had done. Elsewhere, Baek realizes that Lim Sun had been in his office due to the missing razor and CCTV footage.
The next day, while talking to Ko Won, Lim Sun mentions she’s been looking for a cat, and Ko Won posts the missing cat poster Da-yeong had on his social media platform to help Lim Sun. Soon, they receive many leads, one of which seems promising. Lim Sun and Ko Won reach the place, but when Lim Sun meets the person, she realizes it was a fan who just wanted to meet Ko Won.
At the same time, Da-yeong comes across Ji-ung and invites him into her house to talk about Mi-jin. While there, Mi-jin calls Da-yeong, saying she’ll be coming back late. Ji-ung hears a man’s voice and feels alarmed.
He spends the next several hours worrying about Mi-jin and contemplating whether he should use the GPS tracker, but since it’s ethically wrong to use it unless Mi-jin is in danger, he decides against it. He does call Mi-jin, but Ko Won picks up instead while she’s busy searching for the cat in the neighborhood.
Later at night, Ko Won drops Mi-jin home and before parting, he stares at her remembering how he secretly saw her with the annoying fan but instead of getting angry when the fan tossed money at her, she thanked her for being his fan asking her to continue supporting him.
Meanwhile, Byung-duk receives intelligence that the drugs in the club have been moved to Obongsan Mountain.
The next day, Ji-ung calls in the club member he had arrested through the game trap and makes him reveal the location of the buried drugs. To search for the drugs, Ji-ung and Byung-duk travel to the mountain, but due to the difficult track, Byung-duk calls in Lim Sun, who had previously traveled to the top of the mountain in three hours.
It’s revealed that she did so through mountain climbing. While Byung-duk gives up, Ji-ung reluctantly climbs the mountain with her. They meet the naturalist who was one of the witnesses Ji-ung had made Lim Sun visit, and together they find the drugs buried in the mountain. With the drugs, Ji-ung treks down the mountain alone, exhausted, while Lim Sun had already climbed down.
The next day, Byung-duk watches an interview of Ko won talking about his ideal type. He imagines himself attacking him for dating someone twenty years older. While he is watching the video, Ji ung watches the video too, jealous at Ko won’s post where he’s trying to find the cat belonging to someone he cares about. Ji ung is suspicious when Ko won suddenly comes to meet Lim Sun. Ko won takes her away to give her medicine for her health. Byung duk once again witnesses them together. Later, he meets with Ko Won who seems excited and makes Ko Won drink with him, trying to lecture him about the age difference between Lim Sun and him but he ends up getting drunk and saying too much. However, he supports their relationship promising to kill him if he hurts Lim sun.
Ji-ung finally picks them both up. In the car, Ko Won asks Ji-ung about his relationship with Mi-jin, expressing his reluctance to be a third wheel, but Ji-ung doesn’t have an answer. Later that night, Mi-jin recalls how Ji-ung had promised to call her but didn’t. When Ji-ung finally does call her, she’s already asleep with her phone turned off.
The next morning, Lim Sun informs the team that the “drugs from Hwadong Medical Centre and the drugs from Obongsan are a match.” Ji-ung asks Byung-duk to request a warrant. Meanwhile, Ko Won receives another tip about the senior intern with a hidden identity but shreds it instead.
Later in the day, Ji-ung comes to meet Mi-jin, but since both of them are poor at communicating their feelings, there’s another misunderstanding, with Ji-ung leaving and Mi-jin going back home. It starts raining, and Mi-jin goes back to give Ji-ung an umbrella but finds Ko Won there, who confesses to her. Meanwhile, Ji-ung, who was on his way home, suddenly comes back and sees the two together sharing an umbrella as the episode ends.
What are theses two adults doing? Why can’t they admit they already like each other. I hope they don’t make the show boring by dragging things out for too long. Anyway, fingers crossed.