Genius criminal profiler and possible psychopath, Lee Hyun (Seo In Guk) confronts police detective, Cha Ji Ahn (Jang Na Ra) to ask her point blank whether she doubts him, and believes that he’s the same kind of monster as serial killer, Lee Joon Young (Do Kyung Soo or EXO’s DO). Ji Ahn hesitates, but Hyun reads her response from her expression. His face falls as he acknowledges her doubts about him.
Back at the police station, veteran cop, Son Myeong Woo (Min Sung Wook) looks at murder suspect, Lee Jeong Ha’s phone records. His last call was to someone named Lee Jin Woo. Meanwhile, cheerful rookie cop, Min Seung Joo (Kim Jae Young) and geeky cop, Choi Eun Bok (Son Seung Won) spot a suspicious looking guy on CCTV footage from a nearby camera. They spot a possible blood stain on the guy’s clothes. This evidence, combined with Hyun’s discovery of a photo of Jeong Ha and Jin Woo together is enough for team leader, Kang Eun Hyeok (Lee Chun Hee) to send the team to Jin Woo’s school and home.
The atmosphere is awkward in the car, as Hyun and Ji Ahn drive to Jin Woo’s home. Ji Ahn tries to say something to smooth things over (like what? “I only partly think you’re a murderous psychopath?”), but Hyun cuts her off. They’re both saved by the bell when cold-blooded lawyer, Jung Sun Ho (Park Bo Gum) calls from Jeong Ha’s hospital room to report that Jeong Ha has gone into septic shock. Hyun pulls over and kicks Ji Ahn out of the car without comment, then goes to the hospital. By the roadside, Ji Ahn curses herself for ever feeling guilty towards Hyun.
Sun Ho is waiting by Jeong Ha’s bedside when Hyun arrives, and informs Hyun that Jeong Ha is recovering. Hyun leaves Jeong Ha a copy of the children’s book, Wolf Story and tells him that he will catch Jin Woo, the guy Jeong Ha has been protecting. Hyun thanks Sun Ho, but responds coldly to the lawyer’s friendly overture. As Hyun leaves, Sun Ho follows him and asks what kind of relationship he has with Jeong Ha. When Hyun replies that he has no particular reason for liking him, Sun Ho looks strangely hurt.
Jin Woo walks down in the street in his high school uniform and stops to look at kitchen knives in the window of a shop. His finger has a bandage on it, and we learn why as medical examiner, Lee Joon Ho (Choi Won Young) explains that whoever held the knife would have injured their own finger against the blade. Ji Ahn thanks Joon Ho for the information then hangs up. Ji Ahn pulls up to a police van and opens the door, to find Myeong Woo and Eun Hyeok suiting up in bulletproof vests. Myeong Woo asks where Hyun is, and when he learns that he’s not coming, he laughs at Hyun’s presumed cowardice at avoiding situations where he has to come in contact with the culprit. Ji Ahn disagrees, but they’re interrupted when they catch sight of Jin Woo down the road.
Jin Woo takes off running, with Ji Ahn, Myeong Woo and Eun Hyeok in pursuit. When they finally corner him, Jin Woo pulls out a knife and attacks them, but he’s no match for Ji Ahn, who gets him down and in handcuffs in no time.
When they get Jin Woo back to the police station, the accused sticks to the story that he was dragged to the crime scene by Jeong Ha, who was the actual murderer. As Jin Woo waits in the interrogation room, Eun Hyeok and planning officer, Hyun Ji Soo (Im Ji Eun) watch him from the viewing room, and wonder how they’ll crack such a tough case. As per usual, Hyun pops up out of nowhere, and suggests that they turn up the air conditioning, since Jin Woo will be more nervous the colder he gets. When Ji Soo tries to intervene, Hyun sarcastically promises to talk to her later.
Back in the office area, Hyun stops Ji Ahn before she walks into him, and asks what she’s looking at so intently. She’s reading Jin Woo’s records, but Hyun is more interested in confirming that the cut on her lip is from Jin Woo. After they banter about her scarred face, Hyun tells her that he needs her to come along to Jin Woo’s apartment. Gratified at being needed, Ji Ahn agrees to come along.
The truth comes out when they arrive, that Hyun wants her to guess Jin Woo’s computer’s password, since she can relate to the mentality of a violent 18-year-old. Ji Ahn is offended, but he leaves her to it, and analyses the contents of Jin Woo’s room: namely, that Jin Woo is a violent, isolated teenager with anger management issues, who was fixated on his father, and unhappy with his mother. Hyun theorizes that his mother had a tough time with him, just as he discovers Jin Woo’s mother standing in the doorway.
Hyun asks her about Jin Woo’s birth father, and she tells him that Jin Woo didn’t know anything about him, since she didn’t want him to remember that he was a murder victim. She shows Hyun the same articles that he found earlier in Jeong Ha’s apartment.
Meanwhile, Ji Ahn figures out the password for Jin Woo’s computer, and Hyun starts poking around. He logs in to Jin Woo’s email to discover a correspondence with Jeong Ha’s father, convicted rapist and murderer, Lee Hyun Cheol. It turns out that, without any information as to his biological father, Jin Woo believed that his dad was Hyun Cheol. Hyun theorizes that Jeong Ha knew about the misunderstanding, and that’s why he protected Jin Woo.
Back at the hospital, Sun Ho comes back to find Jeong Ha holding Wolf Story. Jeong Ha explains that Hyun used to read this book with his father and brother as a child, and that it’s based on an Indian proverb. Sun Ho knows all about it already, but Jeong Ha can’t keep his eyes open to talk about it further. As Jeong Ha drifts off, Sun Ho wonders what Hyun liked about the younger man.
Back at the police station, they get the news of a partial fingerprint on the knife, just as Hyun comes into the office. His announcement that he’ll get a confession from Jin Woo is met with derision from Myeong Woo, since Hyun has appeared only after the suspect has been caught. Hyun ignores him and proceeds to the interrogation.
In the viewing room, Ji Ahn and the rest of the team watch as Hyun speaks to Jin Woo in the interrogation room. Hyun starts off by listing Hyun Cheol’s long list of crimes, including multiple rapes and murders. He casually calls him trash, provoking Jin Woo into defending Hyun Cheol, calling him his father. Hyun tells Jin Woo that the person he murdered was the witness to Hyun Cheol’s last murder. When Jin Woo defends the murder as justified, Hyun points out that he’s just confessed.
In the viewing room, the confused detectives wonder why Jin Woo is calling Hyun Cheol his father. Ji Ahn explains that Jeong Ha and Jin Woo met at a family support group, where they became close friends. Jeong Ha already knew Jin Woo’s identity as the son of Hyun Cheol’s last victim, and thus was devoted to Jin Woo. Jin Woo found his mother’s file on the murder, but mixed things up, believing that his father was the murderer rather than the victim. Jin Woo visited Hyun Cheol in prison to find out if he was his son.
In the interrogation room, Hyun gives an angry Jin Woo an article about his father’s murder, and asks him to identify which of the men, the murderer or the victim, was his father. When Jin Woo starts to break down, Hyun presses the point, that Hyun Cheol probably used him, since he looked just like his father. Jin Woo used Hyeon Cheol too, to explain his own violent tendencies and anger. Jin Woo breaks down completely as the detectives run into the room, and Hyun walks away.
Back at the hospital, Sun Ho reads the wolf story to a sleeping Jeong Ha, about an Indian grandfather who told his grandson how everyone has two wolves battling in their hearts, one good and one bad. When the grandson asked his grandfather which one would win, the grandfather said, “The one you feed.”
Hyun and Ji Ahn arrive just in time to catch the end of the story, and Sun Ho gives them the news that Jeong Ha has taken a turn for the worst, and isn’t likely to make it. Hyun is stricken, while Ji Ahn drags Sun Ho outside to have some tea. In her mind, Ji Ahn has already figured out why Hyun is so attached to Jeong Ha, since he also doubted himself. When Sun Ho asks what she’s thinking, she refuses to tell him. He wonders how they can become friends, and she replies honestly that it might be difficult. Instead, she hopes that Jeong Ha gets better.
Back in the room, an ailing Jeong Ha confesses to Hyun how hard he tried not to become like his father. As his eyes droop closed, Hyun’s eyes glaze over in tears and he takes Jeong Ha’s hand.
Back at her apartment, Ji Ahn beats her head against her table while her her aunt, Yang Eun Jung (Shin Dong Mi) watches. When Eun Jung asks, Ji Ahn denies being worried about Hyun, but then thinks back to him asking her how she saw him. She launches into a tirade of justifications for her suspicions, until Eun Jung cuts her off. She encourages Ji Ahn to continue suspecting him, since it helped her get through her problems to focus on him instead.
Back at his family home, Hyun gets a call from Ji Ahn instructing him to meet her at a park between their homes in 20 minutes. When they meet, she announces that he’s a rude and obnoxious weirdo, but that she doesn’t think he’s a monster like Joon Young. She trails off and looks away since she’s annoyed to have to admit that, having seen Hyun up close, her assessment is that he’s not that bad. Hyun moves in close and tells her to look at him when she’s talking. He looks relieved as Ji Ahn finally looks him straight in the eye, and tells him that he shouldn’t doubt himself, since she doesn’t. They shake hands, as they agree to be partners, but Ji Ahn starts feeling awkward under his intense gaze. She suggests going to see a movie to break the ice, then immediately takes it back as she realizes what it sounds like. Hyun is amused as she backpedals, but he agrees to go at another time. Ji Ahn practically runs away to get out of the situation, and beats herself up as she rides home.
Hyun grins to himself on his drive, but it turns out his destination is the prison, to visit Hyun Cheol. Hyun Cheol has no idea who Hyun is and why he’s there, and Hyun doesn’t bother to explain himself. Instead, he tells Hyun Cheol about Jeong Ha’s miserable life, doubting everything about himself in the fear of turning into his father. He tells him that Jeong Ha has died by Jin Woo’s hand, and shows him the death certificate. Hyun looks satisfied as Hyun Cheol breaks down in tears, but on the drive back to the prison, he thinks back to Ji Ahn’s words that he’s not a monster and wonders if it is true.
Back at the police station, the entire investigation team minus Ji Ahn is working on the weekend, since they have nothing better to do. They wonder where Ji Ahn is, but it turns out that she is at home, dressing up for her movie with Hyun. At the last minute, she changes from a date worthy dress to her usual outfit, then goes to the movie theatre to meet him. When Hyun arrives, she tells him that they can’t go to the movies, since there’s none he would like. He quickly realizes that she knows his taste from stalking him, and agrees when she suggests they go out to eat. They have the same problem again, since he’s picky about where he eats. Hyun tells her to disregard his preferences, and to pick where she wants to go. Predictably, Ji Ahn picks something he would hate: an amusement park. Hyun hesitates, but she drags him along.
The amusement park turns out be one that Ji Ahn used to go to with her father, but has since shut down. She drags Hyun around the place, and forces him to take pictures, but his torture is interrupted when he spots someone following them. When a butterfly floats by, Ji Ahn stops to look, and Hyun caresses her on the head while she’s distracted. She’s obviously touched, as he empathizes with her about the tough times she must have had growing up.
That evening, Ji Ahn looks happy as she goes to bed. Hyun, meanwhile, remembers the mystery he’d briefly forgotten, namely his neighbour, Joon Ho. Ji Ahn is jolted out of her happy reverie by Hyun’s call to ask for Joon Ho’s handwritten autopsy report before he abruptly hangs up. Hyun is preoccupied with the other mystery of the day; he thinks back to their wander through the amusement park when, on the pretext of going to the washroom, he unsuccessfully chased the mystery man who had been following them.
Meanwhile, Sun Ho receives pictures taken by the mystery man of Hyun and Ji Ahn’s trip to the amusement park (or date? Can we call it that?), and is surprised to find that they were closer than he had assumed. He thinks back to his conversation with murderer, Yang Seung Hoon (Tae In Ho), swearing vengeance against the two of them from a Chinese prison. Sun Ho asks his secretary to get in touch with Seung Hoon’s Chinese lawyer to put him in touch with Director Yang. It is unclear if he is referring to Seung Hoon or the man’s father.
Meanwhile, Hyun is bothering his art dealer friend again, this time to perform background checks on Eun Hyeok, Myeong Woo, Eun Bok, Seung Joo, Joon Ho, and Sun Ho. When his friend protests, he reminds him of his debt, then tells him he’s almost done repaying it. When his friend asks why he wants to look into these people, Hyun says that at least one of them is a murderer. Hyun almost takes Myeong Woo off the pile, but leaves him in, since they’re doing the background check anyway.
Sun Ho is on the phone with Director Yang, and he offers the advice that they take care of Ji Ahn now, and that he’ll personally take care of Hyun later. As he leaves the room, we see a painting of two men with the logo of an infinity symbol with two eyes intertwined.
Ji Ahn goes shopping at the grocery store, where she runs into a casually dressed Sun Ho. Sun Ho is friendly as they exchange greetings, but Ji Ahn keeps it short and moves on. Later, in the parking lot, when her car won’t start, Sun Ho appears again and offers her a ride home. When he drops her off, he offers to help her carry her bags, but she turns him down and runs off.
Back at his house, Hyun finds a red envelope in his mail with a drawing of a blood spattered car inside. Meanwhile, Ji Ahn opens the door to her apartment, but is interrupted by the arrival of a mysterious man.
So, the show has now doubled down on making us suspect everyone of being a murderer. I’m going to call it right now and say that Sun Ho is a red herring, and that the real murderer is someone else. Maybe one of the detectives? Maybe Joon Ho? Who knows? But, Sun Ho seems a little too obvious, frankly. He may be Min or he may not be Min, but I don’t think he’s the murderer that Hyun is looking for.
Meanwhile, on a more shallow note, how good did Hyun and Ji Ahn look on their date? I’m beginning to find them really entertaining together, what with Hyun’s crankiness and propensity towards direct eye contact, and Ji Ahn’s blunt honesty. The fact that she’s fighting her attraction to him is doubly cute. Sadly, we have barely any idea how he feels about her, aside from the fact that he doesn’t want her to think that he’s a monster.
But, Hyun is definitely a more complicated character than at first glance. In the first few episodes, he was presented as a pretty cold-blooded guy, but looking at his confrontation with Hyun Cheol and his “date” with Ji Ahn, it’s clear that a lot more runs beneath the surface.
I’m a little sad that this show isn’t more popular than it is, because it’s really shaping up to be, if not a game-changer, then at least, a fun mystery romance.