Da-mi, a young high school student with a heart condition, leaves her adoptive parents to live with Geum La-hui, her biological mother. When Da-mi arrives at La-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, Mo-ne 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.

Mo-ne 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 Mo-ne and creates the last escape game just for the seven sinners.