Ji-won believed that Su-min would always have her back until she discovered that Su-min was having an affair with her husband. Ji-won, a terminally ill cancer patient, witnesses the two in bed discussing her insurance payout. She ends up not being able to live out the remaining days of her numbered life before she's killed... But then she suddenly wakes up, and it's 2013?!
Ji-won has gone back 10 years in time and learns that events will unfold as they are meant to according to the law of destiny. In an attempt to pass on her fate to Su-min, she tries to set up her future husband, Park Min-hwan, with her... However, Su-min's sly manipulation becomes more apparent to Ji-won, and now it's her turn to counterattack!
Yu Ji-hyuk had no connections with Ji-won in her previous life, but he is gradually becoming involved in her current life. Su-min invites Ji-won to a school reunion to resurrect the shameful memories of when she was ostracized in high school. Ji-won sees through Su-min's intentions, and with the help of her colleagues, she undergoes a transformation.
Ji-won attends an event with Ji-hyeok and meets someone who will be a future topic of discussion. Ji-hyuk becomes concerned as he observes Ji-won's transformation. After a heated encounter at the high school reunion, Su-min becomes even more obsessed with Ji-won. Meanwhile, as Ji-won tries to provoke Su-min with Min-hwan, she unexpectedly discovers a secret about Ji-hyuk during a work errand.
Ji-hyuk reminisces about his first encounter with Ji-won eight years ago. His sole purpose in coming back is now Ji-won. Su-min manipulates Mr. Kim to steal Ji-won's proposal, while Ji-hyuk tries to assist Ji-won. However, due to misunderstandings stemming from his relationship with Hui-yeon, Ji-won ends up getting angry at Ji-hyuk instead.
Ji-hyuk confesses his feelings to Ji-won, but she has no time to contemplate her own emotions for him. As Ji-won attempts to overcome her destiny and confront forces opposing the original direction of her fate, her name is ultimately omitted from the proposal. Ji-hyuk empowers Ji-won to take a stand and fight, while Ji-won recalls a future known only to her.
The two have discovered that they both traveled back in time! While Ji-won is thrilled to find a comrade, Ji-hyuk starts to avoid her. He suffers alone after learning of the cruel laws of time travel too late. Meanwhile, Ji-won goes on a picnic with Su-min and Min-hwan, managing to leave the two behind. On her way back, she runs into Ji-hyuk, who appears to have sorted out his thoughts.
During the company's autumn workshop, Ji-won and Su-min engage in a fierce battle of wits. It's the first time they confront each other so sincerely. Su-min becomes angry and attempts to cross the line to hurt Ji-won. Eventually, an incident occurs at a supermarket tasting event involving Min-hwan.
With Ji-hyuk's help, Min-hwan proposes to Ji-won. Ji-won spreads rumors at work to start a buzz. Su-min is upset and intentionally tries to turn Min-hwan's mother and Ji-won into enemies to ruin the engagement dinner. However, the night of the dinner arrives, and it's the day Ji-won has been waiting for.
Ji-won ruins the engagement dinner, leaving Min-hwan utterly embarrassed. Employees soon gossip that Ji-won and Min-hwan's engagement has been called off, and he's been cheating with Su-min. Su-min tries to cover it up, but because of her lies, the supermarket incident resurfaces. She's now caught in a crisis and ends up dropping the bomb.
They finally kiss. Ji-won is going full power towards him, while he continually tries to hit the brakes. Eventually, he ends up opening up to Ji-won. On the other hand, Su-min and Min-hwan speed up the wedding due to an unexpected pregnancy, and Ji-won shows up with Ji-hyuk as her date, aiming to outshine the bride.
Ji-hyuk's fiancée, Yu-ra, makes an appearance and creates a rift between Ji-hyuk and Ji-won. Moreover, Ji-won is surprised to hear about Ju-ran's stomach cancer. She is shocked to realize that her fate wasn't passed on to Su-min. Meanwhile, Su-min and Min-hwan, spending their newlywed days discontentedly, acquire information about Ji-hyuk that enrages them.
After an accident that was intended to harm Ji-won, Ji-hyuk gets injured instead and falls into a coma. Ji-won is scared that Ji-hyuk may never wake up. With everyone involved in the accident busy covering their tracks, Ji-won learns the truth behind the accident and seeks out Su-min to confront her memories from a distant past.
Ji-hyuk regains consciousness and quietly trails the person involved in the accident that Yu-ra is trying to conceal. Meanwhile, Ji-won realizes that, in order to pass on her fate to Su-min, she must get Min-hwan to have an affair. Ji-won decides to become Min-hwan's secret lover, pretends to break up with Ji-hyuk, and approaches Min-hwan once more.
Su-min meets Yu-ra and presents compelling evidence, prompting Yu-ra to start finding a way to resolve the situation once and for all. Ji-won and Ji-hyuk initiate their final operations toward Min-hwan and Su-min, finally bringing about the night of destiny!
With Su-min's disappearance after Min-hwan's death, the fate intertwined with Ji-won finally dissolves. Ji-won receives a formal invitation to Chairman Yu Han-il's home and starts planning her future with Ji-hyuk. Just as they are about to attain their happiness, Su-min reappears to conclude the long-forged tragic fate.
