Ji-won acreditava que Su-min sempre estaria do seu lado até descobrir que a amiga estava tendo um caso com seu marido. Ji-won, uma paciente com câncer terminal, flagra os dois na cama falando do seguro que receberiam pela doença dela. Mesmo com os dias contados, ela acaba não vivendo o que restava de sua vida e é morta... Mas, de repente, ela acorda, e o ano é 2013!

Ji-won volta dez anos no tempo e descobre que tudo que deve acontecer vai acontecer, conforme as leis do destino. Na tentativa de transferir seu destino para Su-min, ela tenta fazer o futuro marido Park Min-hwan e a amiga ficarem juntos... Mas as manipulações de Su-min se tornam mais claras para Ji-won, e agora é a vez dela de contra-atacar!

Yu Ji-hyuk não tinha nenhuma ligação com Ji-won na antiga vida dela, mas começa a se envolver aos poucos em sua vida atual. Su-min convida Ji-won para um reencontro do colégio para despertar lembranças humilhantes de quando ela era hostilizada pela turma. Ji-won percebe as intenções de Su-min e, com a ajuda de colegas, passa por uma transformação.

Ji-won participa de um evento com Ji-hyuk e encontra alguém que será tema de uma discussão futura. Ji-hyuk fica preocupado diante da transformação de Ji-won. Depois de um encontro acalorado no reencontro do colégio, Su-min fica ainda mais obcecada por Ji-won. Enquanto Ji-won tenta unir Su-min e Min-hwan, ela acaba descobrindo um segredo sobre Ji-hyuk quando sai para um compromisso profissional.

Ji-hyuk relembra seu primeiro encontro com Ji-won oito anos antes. Agora ela é o único motivo para ele ter voltado. Su-min manipula o Sr. Kim para roubar a proposta de Ji-won, enquanto Ji-hyuk tenta auxiliar Ji-won. Mas, devido a um mal-entendido quanto à relação entre Ji-hyuk e Hui-yeon, Ji-won acaba ficando com raiva dele.

Ji-hyuk se declara para Ji-won, mas ela não tem tempo para refletir sobre os próprios sentimentos em relação a ele. Enquanto Ji-won tenta superar seu destino e confrontar forças em oposição ao rumo original de sua vida, seu nome acaba sendo omitido da proposta. Ji-hyuk encoraja Ji-won a se posicionar e lutar, e ela se lembra de um futuro que só ela conhece!

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.