A man named M invites seven people to a murder game party hosted by his boss, known as K. As soon as the game begins, M is shot by an unknown perpetrator, which turns the game into a real crime scene. They soon realize that the murder is related to an operation called "Project D", in which they are also involved in. Using the tarot cards given by a gypsy as their clues, the seven witnesses must attempt to find the culprit before it reaches the next victim.

Guests: Yoo Yeon-seok, Kangnam, Kim Jung-tae, ^[13] Lee Jae-yong, Park Na-rae, Ye Ji-won ^[14]

After being recruited by K, the amateur detectives travel to Jeju Island in order to help a museum director retrieve an artifact that belonged to his deceased friend. With the help of a local news reporter and a tourist from Seoul, they embark on a treasure hunt around the island. Meanwhile, K reveals that, in the past, an error in the chip that was implanted in the detectives had caused them to slowly lose their memories, which led him to abandon Project D.

While on a vacation in Jeju Island, Kwang-soo wakes up with a hangover and finds a dead woman in his room. Fearing that the police will brand him as a suspect, he flees the scene and decides to find the murderer himself. The six other detectives receive a call from K, saying that Kwang-soo has become a murder suspect. This leads them to investigate the case in an effort to prove his innocence, or else they would have to arrest him.

Jong-min encounters a child who gives him the diary of a teen girl. He finds out that the girl had recently died at Songdo Central Park under mysterious circumstances and receives a call from K, who tells him to gather the detectives at the high school where she attended to look into her death. During the investigation, the detectives discover that her friends have been receiving text messages from her even after she died.

An ex-criminal, whom Jae-wook had arrested during his days as an agent, tells him that a woman was murdered in his hometown, a small island near Incheon. When the detectives go to the island, they discover that the residents believe that a vampire lives in the island and kills a woman whenever anyone tries to investigate on the murders happening in the village. Meanwhile, K tells them that one of the doctors involved in Project D was from the same island.

Two rival curators of an art museum enlist the help of K's detectives and the Genius Detective Team in an attempt to outshine each other. The competition between the two teams becomes fierce as they must find the self-portrait of a recently deceased artist before the painting is auctioned off on the same night.

The detectives attend a magic show rehearsal to support Se-hun, who would be opening the show with a dance performance. During the rehearsal, the magician mysteriously disappears while performing one of his tricks, which sends the crew in a panic as the show would be happening in a few hours. As a result, the director asks the detectives to find him before the show begins.

A man claiming to be K's old friend challenges the detectives to solve a 20-year-old case through a series of tests in order to measure their skills in criminal investigation. Each test has a different goal, and the first detective to complete a test is rewarded with a large sum of money. The man also promises to provide the passcode for the box that the detectives had obtained in Jeju Island, which contains valuable information about Project D. Outside the mission, Se-jeong is seen leaving flowers for M at a columbarium.

Yeon-seok turns himself in and requests that K's detectives should be the one to transport him to prison. Although this confuses the detectives, they accept his request in exchange for information about Project D and his involvement with it. While on their way to prison, Jae-suk receives a phone call from an unknown man demanding Yeon-seok to be brought to him, or else, a bomb that he planted onto a stranger's bag will be detonated.

The detectives receive a scheduled message from K that was written three months ago, during the planning of the murder game party. He tells them that a final test for them is waiting at a safe house in Incheon. However, they also receive a message from a familiar voice saying that he has kidnapped K.

K's detectives find themselves chained and trapped in separate rooms. When they manage to get out, they find Jae-suk, who explains that he survived the explosion and has since been watching over them secretly. Under the guise of Tartarus, he and K created the missions to test their ability to work as a team. Things do not go as planned when the detectives realize that Kwang-soo has disappeared with a mysterious microchip and that K has been murdered by a serial killer called the "Flower Killer".

With C being a potential suspect of K's murder, the detectives visit the psychiatric hospital where he is confined only to discover that he escaped. They find his body at the office of Stephanie Lee, a profiler who frequently visited C, and notice that his wounds are the same as K's. After numerous investigations, they realize that someone is murdering Project D's researchers to seek revenge.

A client recruits the detectives to ensure the safety of the Odd Eye, a family heirloom, before the Phantom Thief steals it first. Meanwhile, K's detectives have decided to open a position for a new member. Yook Sung-jae, a new intern with a cocky personality, helps them with the mission.

While the detectives wait for their client, a new applicant, Hani, arrives and they immediately take a liking to her. However, they discover that she has also applied to be a part of the Genius Detective Team, who soon show up at the same place. With Hani joining the Genius Detectives, the rival teams once again try to outdo each other to win a portion of a shaman's lottery winnings.

K's detectives cautiously welcome former detective Lee Seung-gi into their team after he gains them a client. A supposedly simple investigation becomes complicated when they discover the client's body inside her house, with her neighbor being the prime suspect. They also discover that this neighbor is a fan of the Flower Killer and their murders.

Guests: Kim Dong-jun, Tae Hang-ho [ ko], Min Sung-wook [ ko], Kim Min-jae

A distressed girl sends her friend's urn to Jae-suk and believes that she died by murder instead of committing suicide. The detectives visit her hometown called Guiyi Village in the South Jeolla Province to investigate her claim. There, they notice that there are no men in the village and that, except for the shaman, everyone is deaf. They soon realize that all the young girls have disappeared and supernatural occurrences seem to happen around them. They also discover that Stephanie is the shaman's daughter.

With a large amount of money involved, the detectives split up into different alliances to help three chaebol sons find the will of their late father. One of them is revealed to be Sergeant Kim Min-jae, who has been distancing himself from the family out of shame. While on the way to one of their missions, he discloses that K's autopsy report shows that he had died of poisoning long before he was stabbed, implying that someone else had murdered him.

While Se-jeong and Min-young are nowhere to be found, the male detectives are invited to shoot an episode of the Curious Detective Show with Iz*One. They are tasked to solve the fictitious abduction of two of their members, but they soon realize that someone has kidnapped them for real. The detectives gradually discover that this case connects to their past investigations, as well as to forensic investigator Yoo Jong-hoon, Stephanie, and the Flower Killer.

The detectives secretly attend to initiated an interactive role-playing mystery game called Killosophy using an invitation given to them by Stephanie. The game is a reenactment of the Flower Killer's murders, including K's, and those who are invited are his worshippers called "Sophias". By following each murder, the detectives are able to collect clues that lead them to the identity of the serial killer.

The detectives investigate the suspected Flower Killer's house and find Stephanie dead in a hidden room. With the Flower Killer watching them, they receive photos showing Jong-hoon and Detective Im Won-hee being held captive, and the latter explains that he and Stephanie created Killosophy to lure the Flower Killer. The detectives then receive a video from the culprit, which leads them to a desolate place with murals of flowers. There, they discover the truth behind the murders they have encountered so far.

The son of a deceased mystery author asks for the detectives' help to find out which of his housemates has been stealing his food. Thinking that the case is easy, Kwang-soo believes it to be the perfect time to rejoin the team, which annoys the detectives. They soon realize that the case is much more complicated and everyone in the house is hiding something suspicious. Meanwhile, Seung-gi asks Jong-min to meet him in an unknown area where they are chased by a group of men. While trying to escape, Seung-gi is run over by a truck and is sent to a hospital, where he and Jae-suk meet again.

The detectives split up when they are hired to solve two cases on the same day. One team is tasked to find out what happened to a professor who was starved to death, while the rest attempt to solve a murder in a gambling den. Various clues and evidence lead both teams to believe that the cases are linked to the murder of Gruntrack, one of the housemates from the previous case. Meanwhile, Seung-gi is diagnosed with selective amnesia and does not remember himself as the Flower Killer. Though the detectives are initially against it, they let him join the team as they think that his life could be in danger.

When the detectives discover a mysterious website that claims to guarantee humans a place in heaven, Se-jeong and Min-young decide to use themselves as bait to uncover the truth behind the website. They find out that the website lures vulnerable women into an abandoned hospital and kills them to sell their organs and body parts. While one of the culprits are caught and escorted by the police, an unknown sniper shoots and kills him.

Nam Uk-gun, CEO and heir to a high fashion brand, decides to hold a party in an attempt to look for Seonnyeo, his childhood friend and fiancee. However, he had last seen her as a child and has forgotten what she looks like. He hires the detectives to look for the real Seonnyeo among the girls at the party so he can marry her, which was his grandfather's final wish.

The detectives receive a package containing a flash drive with a video. In it, different footages and photos of an old crime scene appear. A sudden broadcast signal intrusion was hijacked around the country, shows a footage of a masked man holding a woman hostage. Addressing the detectives directly, he threatens them to solve the case in the video, or else, he would kill the woman. Because of the limited time given to them by the masked man, the detectives enlist the help of users in an online forum.

Min-young meets with the team while holding a bouquet of cistus sent by their client. The same client sends them a letter, who tells them that he would have died by the time they receive the flowers. While investigating the case, Seung-gi confides in Jae-suk about his whereabouts before his amnesia: he discovered that a large organization with a scale symbol has been killing criminals involved in the detectives' past and present cases. Because of this, Seung-gi (as the Flower Killer) is one of its targets. He also discovered that one of the detectives is a member of the organization, which lead him to fake his amnesia so he could rejoin the team and find out who it is.

After being confronted by an angry client, the detectives realize that someone has been impersonating them to scam clients. At a cafe, they meet another client, who is possessed by a ghost, as well as a group of people pretending to be them. With both teams claiming to be the real detectives, they go against one another to solve the case. Midway through the investigation, each team notices that one of their members is missing. The culprit of the case is also shot by a sniper. When the detectives go to the rooftop where the sniper would have been, they find a note from Hwalbindang, the secret organization who responsible for killing the criminals. The note tells them that Seung-gi, the Flower Killer, will be killed next.

The detectives suspect that Min-young may be working for Hwalbindang and they go to an abandoned village full of traps to find her. Seung-gi decides to face Min-young himself and leaves the others during the search. Meanwhile, the detectives find the flash drive that Kwang-soo stole when he disappeared. It contains a list of potential criminals, which was gathered by Project D, and includes Min-young. On the computer screen, Hwalbindang's godmother reveals that she has killed Seung-gi and is planning to eliminate everyone else on the list. With only an hour given to them, the detectives must find a way to get to Min-young before a bomb is detonated.