Da-mi, a young high school student with a heart condition, leaves her adoptive parents to live with Geum Ra-hui, her biological mother. When Da-mi arrives at Ra-hui's place, she is overwhelmed by her riches. However, she soon starts to wonder if her mother's intentions are genuine after an incident with her affluent grandfather.

After a humiliating incident at her new school, Da-mi faints in front of Chil-sung's house. Meanwhile, Mo-ne attracts the attention of multiple entertainment agencies after a stunning audition, including La-hui. However, a rumor surfaces online that could potentially destroy everything she has worked for.

Da Mi leaves La Hui and promises she won't let her receive any money from her grandfather. Meanwhile, Scarlet Letter spreads rumors of Da Mi and her stepfather's promiscuous relationship, causing widespread outrage and chaos. To make things right, Da Mi takes things into her own hands and calls everyone to the park.

Da Mi disappears as she broadcasts getting shot live over the Internet, and the person taking the fall is her adoptive father, Lee Hwi So. The people involved get entangled in twisted turmoil while the police search for Da Mi's body. Meanwhile, Bang Chil Sung steps in to find the truth.

Lee Hwi So gets the death sentence for the murder of Da Mi and Chil Sung. Miraculously, Bang Chil Sung survives the fall and works with Kang Ki Tak to secretly help Hwi So get out of prison so he can avenge Da Mi's death. Meanwhile, Mone becomes a huge star and prepares a special party on Jeju Island to which only thirty-three winners are invited.

After encountering peril and beating death, the seven people who managed to escape the island alive struggle to stay out of facing trouble with the law. However, all seven of them find a threatening message in their room that shocks them. Meanwhile, Matthew Lee appears just in the nick of time to help the seven survivors with the police investigation.

After learning that Nam Chul-woo was the detective in Da-mi's murder, La-hui senses something out of place and gets Jin-mo to check on Lee Hwi-so. Meanwhile, Mo-ne's guilty conscience haunts her while her relationship with La-hui deteriorates. Later, Matthew gathers the seven survivors and watches them struggle and blame each other for their survival.

After another death to cover up the incident on the island occurs, Matthew determines to use the Seven to find the mastermind behind it all. Meanwhile, another suspicious letter arrives to each of the Seven with their darkest secrets, causing chaos within the group. They come together to form a plan and go after Chairman Bang, who they learn is still alive.

After the TIKITAKA Signing and Inauguration, Matthew hosts a party to celebrate and invites those seven survivors to his home. Meanwhile, Matthew manages to bring Mo-ne's family back to Seoul, and Ji-a threatens Mo-ne about Sim Jun-seok.

The seven criminals find Ji-a's dead body at her place and straight away realize K is behind it. While they are in panic, Jin-mo gets a phone call from K. Meanwhile, Matthew decides to take everything away from those seven criminals and reveal their crimes to the public, one by one.

The seven people find out Matthew is Hwi-so, and Do-hyuk has been helping him all this time. He plans to use the seven people as his pawns to fight K and Sungchan Group. He lets them choose whether to die in K's hands or gain the chance to make amends by standing on his side.

Chairman Sim of Sungchan Group notices TIKITAKA has been challenging him from the beginning. Chairman Sim looks into Matthew and Do-hyuk to fight them back. Meanwhile, Matthew and Do-hyuk are suspicious of Ki-tak and are confused about which side he is on.

Do-hyuk thinks Ki-tak betrayed him and Matthew without realizing that Matthew was behind everything. Matthew lies to Do-hyuk that Ki-tak is dead when, in fact, he was holding Ki-tak captive. Matthew, who revealed himself as K to Ki-tak, tortures Ki-tak to find out where Chairman Bang’s money is. Meanwhile, Jin-mo reveals to Matthew that K’s child is alive.

Matthew threatens Jin-mo that he’ll kill Paeng-hee if Do-hyuk ever finds out that he’s K. Do-hyuk barges into Sungchan to find out where Ki-tak went, and he ends up hurting Mo-ne who was there to see the chairman Sim. Meanwhile, another mission is given to them, and this time, they must steal the paintings from Sungchan Gallery.

Mone helps Do Hyuk escape while he’s being chased by the police, and they run away together. Do Hyuk finds out the identity of K and infiltrates the TIKITAKA building to get him. La Hui accidentally finds where Lee Hwi So is. Meanwhile, Chairman Sim decides to use Do Hyuk and blame him for all the crimes.

Chairman Sim and Min Do Hyuk’s paternity test results shock the entire nation. Matthew goes to Chairman Sim’s house and lures Do Hyuk there. Chairman Sim throws himself in front of Do Hyuk to stop Matthew from killing him. Cha Ju Ran and Nam Chul Woo manage to break into Chairman Bang’s vault and find his money.

Chairman Sim holds a press conference and reveals the truth about Sim Jun Seok. La Hui plans to team up with Ju Ran in order to get away with the life-or-death situation. Meanwhile, K finds out Do Hyuk's hideout through Mone and creates the last escape game just for the seven sinners.

The six that held hands with K, the absolute evil, for survival at the crossroads of good and evil live lavish lives in return for Min Do Hyuk's betrayal. However, they are slaves to K and have lost their freedom. Meanwhile, Min Do Hyuk opens his eyes out of a coma he fell into from the explosion he suffered on the rooftop.

Matthew promotes TIKITAKA's new missing children application, Children Home. During the campaign, Myoung Ji's daughter, Erica, gets abducted. Meanwhile, the movie preview is just around the corner, and Monet worries that the mistakes she made in her life will get exposed to the world. Although she tries to stop the preview from showing, the preview event opens its doors.

Min Do Hyuk removes his mask and shows himself to Sim Jun Seok, who can't believe he is alive. He is furious that Do Hyuk's trickery got him to clear the charges against him, and he gathers everyone to uncover the traitor. However, Do Hyuk makes his move by winning the hearts of the public, who go crazy over him and his story.

After rescuing No Han Na, Min Do Hyuk's plan to ensure her safety has Matthew scrambling to find her. The whole country watches as the remaining time runs out. Matthew accuses Mone of working with Min Do Hyuk but gives her a chance to prove her life is worth keeping. Meanwhile, Hwang Chan Sung watches Mone closely with a helping hand.

At Mone and Chan Sung's engagement party, Matthew tries to get close to Chan Sung, but Chan Sung shuts him down. With Chan Sung at her back, Mone exposes how La Hui and Matthew had kept their eyes on her. Meanwhile, Do Hyuk and Ki Tak break into Matthew's secret room and access LUCA to gain critical data for their next attack.

La Hui risks getting exposed and stops Matthew from killing Do Hyuk and Ki Tak. Matthew believes Chan Sung is Medusa and puts Mone on her second mission. Meanwhile, Chan Sung reveals himself as Medusa to Do Hyuk and asks him to join hands against Matthew. However, Do Hyuk senses something isn't right.

Geum La Hui takes matters into her own hands after getting revealed as Medusa. She begins to trap those involved in Da Mi's death one by one, and ultimately herself, to be judged and punished. Meanwhile, Min Do Hyuk continues to help Mone, which disturbs Chan Sung.

After leaving a letter for Ki Tak, Geum La Hui starts the game of survival that she plans to broadcast live over Save's network. However, Chan Sung has plans of his own and takes advantage. Meanwhile, Ki Tak races to stop La Hui and save Do Hyuk after he reads La Hui's letter of regret.

The Seoul mayor by-elections are nearing, but Yang Jin Mo trails behind in his campaign. Luckily, Hwang Chan Sung lends his help for something in return. Meanwhile, Mo Ne succumbs to Chan Sung to locate her mother, who she thought was dead, and Do Hyuk reclaims Sungchan Group to take on TIKITAKA and Save.

After the wedding, Mo Ne can't believe what she discovers at Chan Sung's house and hopes she can save her mother. However, she can only succumb to Chan Sung's demands and rely on Min Hyuk with a plan. With Han Na in Chan Sung's hands, Jin Mo seeks help from Min Hyuk and twists Matthew's plans. Meanwhile, Min Hyuk uses Ju Ran and Chul Woo to turn Matthew and Chan Sung against each other.

After getting shot by Matthew, Go Myoung Ji struggles to hang on to her life with Jin Mo and the rest of the people by her side. Meanwhile, Matthew finds a way to escape police custody with Chan Sung's help and tries to manipulate the public in his favour. Later, Do Hyuk and the rest commit to a press conference to expose their sins and corner Matthew.

Matthew tries to stop Min Do Hyuk's press conference, but it's too late. However, he doesn't give up. Meanwhile, the reporters agree to reveal the evil deeds that stemmed from the Bobble incident and promise to expose Matthew's true identity. Later, Min Do Hyuk becomes Sungchan Group's chairman and reveals himself as Chairman Sim's biological heir.

Do Hyuk pushes forward with his plans to expose Matthew and starts by releasing S-CURI, an app that safeguards users' secret chats from being spied on. Matthew pours all his effort and money into proving his identity as Lee Hwi So. Meanwhile, Mone works with Do Hyuk to turn Chan Sung against Matthew.

Yang Jin Mo dies. He leaves his heart for Go Myoung Ji and saves her life. Matthew uses his power and connections to make Min Do Hyuk look like Yang Jin Mo's murderer. Meanwhile, Min Do Hyuk comes up with a new plan, and Han Mo Ne is there to help him.

Despite Mo Ne's involvement in Da Mi's death, Ki Tak saves her from Chan Sung's wrath and keeps her out of harm's way. However, Ki Tak gets taken hostage by Matthew as she makes her getaway. Upon discovery of Chan Sung's murder, Matthew gets the upper hand by framing Do Hyuk as the murderer and destroys his plan. Meanwhile, Myoung Ji recovers and plots her revenge.

Min Do Hyuk corners Matthew and exposes the truth behind all his evil deeds in front of the press as his final blow. With no way to escape the accusations, Matthew takes matters into his own hands, creating carnage. Meanwhile, Mo Ne turns herself in as Chan Sung's murderer, and the prosecution goes after Matthew.