Choi Sang-eun gives customized marriage contracts for singles needing a marriage. After 13 years in the business, she wants to retire but finds it hard to end it with Jung Ji-ho, a long-term customer of Mon, Wed, and Fri. They’ve been together for 5 years, but she knows nothing about him and delays ending their contract. Meanwhile, superstar Kang Hae-jin moves in the top floor of Ji-ho’s house...

Sang-eun's hurt by Ji-ho asking to end the contract first. She delays it giving a flimsy excuse. She's strangely upset with him and is confused by it. Meanwhile, Hae-jin sees his first love Sang-eun who disappeared 13 years ago after leaving a strong impression but is shocked she is Ji-ho’s wife. To make the matters worse, he witnesses Ji-ho’s strangeness and believes that she is in danger...

Sang-eun, Ji-ho and Hae-jin have a three-way encounter at the mansion. J-ho reveals his identity to Hae-jin due to his suspicion. Sang-eun gets to know Ji-ho a little bit more but despite what she wants the time to end the contract comes. When the contract ends, restless Sang-eun visits Ji-ho with divorce papers as an excuse to see him but is attacked by a mysterious armed man.

Sang-eun's surprised at Ji-ho giving her concert tickets, not divorce papers. They extend their contract as they run into his senior judge and his wife. Madam Yoo is in big trouble after seeking a comeback after losing everything 13 years ago due to Sang-eun. Sang-eun saves her and give up her retirement despite her love-hate relationship. Meanwhile, Hae-jin gets into trouble from a false rumor...

Sang-eun is angry at Hae-jin. Hae-jin asks Sang-eun to take him as her customer. She is torn seeing him vulnerable and eventually, she accepts his offer. Ji-ho feels uncomfortable about their contract. Sang-eun tries to clear up the misunderstanding but is not easy. Meanwhile, Madam Yoo is released from the detention center and stays at Sang-eun, and their uncomfortable living situation begins...

Sang-eun needs to settle a contract with Hae-jin. After some quarreling, Ji-ho's day is Mon, Wed, and Fri and Hae-jin on Tues, Thur, and Sat. And the alternate day marriage begins. Meanwhile, Sang-eun and Ji-ho prepare a housewarming party for his work. While decorating the house they develop feelings. At the housewarming party, Sang-eun drinks too much and gets a serious blackout the next day...

Sang-eun remembers her first kiss with Ji-ho but is upset as Ji-ho seems indifferent. They hide their feelings causing their relationship to be awkward. As Hae-jin uses work as excuse and goes on a date with Sang-eun, he’s feelings towards Sang-eun grows even more. Meanwhile, Madam Yoo visits Ina group and threatens to take back Sang-eun into their family again…

Ji-ho tries to find a way to express his feelings toward Sang-eun. During a couple’s golf gathering, he doesn’t hold back to show kindness and care towards Sang-eun causing her to have mixed feelings about him. Meanwhile, Hae-jin happily waits for Tues, Thurs and Sat but gets into a big fight with Ran-hee who questions about Sang-eun. He then collapses in front of Sang-eun due to extreme stress.

Sang-eun meets Ji-eun, ex-wife of Ji-ho and a legal advisor of Hae-jin. Ji-ho says no more than there’s nothing between them but Sang-eun’s thoughts gets tangled. After filming, Hae-jin misses Sang-eun and visits her but drunk Ji-ho appears and three of them have an awkward gathering at the beach. When Ji-ho witnesses Hae-jin and Sang-eun being close, he appears to be bothered for the first time…

Ji-ho and Sang-eun realized their feelings for each other and he surprises his co-workers by coming to work very differently than usual. Sang-eun tries to end the contract with Hae-jin to focus her relationship with Ji-ho and Hae-jin tries to give up his feelings for her but finds it difficult. Meanwhile, Ji-eun finds out Sang-eun had contracts with both Hae-jin and Ji-ho and visits Ji-ho’s house…

Sang-eun worries about Ji-ho as she is exposed to the public. Ji-ho’s senior informs about his promotion but doesn’t tell Sang-eun. Sang-eun tells Gangjin group’s family she doesn’t want to marry Hae-jin. Ji-ho makes questions for Sang-eun and they have a great time. While Hae-jin’s at the police station due to his clash with Sang-eun’s stalker. Sang-eun’s in shock when the stalker is revealed…

Sang-eun’s 12th marriage is unveiled causing controversy and she insists she’s at fault to protect Hae-jin. She asks Ji-ho to have some space due to this. Ji-ho and Hae-jin is upset seeing Sang-eun trying to bear everything. Ji-ho hears from Gwang-nam of Madam Yoo’s provocation to Sang-eun and investigates her and Ina group. Hae-jin prepares a conference to squelch criticism towards Sang-eun…

Sang-eun rushes to the hospital in shock when she hears of a mysterious car accident. Ji-ho comforts her and they become closer. Hae-jin makes a formal announcement of his breakup with Sang-eun. Chairman Ganjin tells him to join Gangjin group. Seon-jin feels threatened and uses Sang-eun to ingratiate himself with his father. Meanwhile, Ji-ho questions the car accident and starts investigating…

While Sang-eun and Ji-ho have a lovely time dreaming of their future together, people ordered by Seon-jin secretly break into Sang-eun’s house. Hae-jin learns of this and tells Madam Yoo of Seon-jin’s scheme to use Project Jamie. Madam Yoo decides to take all the blame to protect Sang-eun and Ji-ho goes against his principle for the first time to stop her…

After that day, Ji-ho waits for Sang-eun who didn’t turn up. Sang-eun doesn’t have the courage and hesitates and Ji-ho returns to his cold self. The co-workers become more worried seeing Ji-ho being so emotionless. Meanwhile, Sang-eun realizes her feelings through honest advice from Gwang-nam and Madam Yoo…