Ban Ha-Ni (Choi Gang-Hee) is 37-years-old and a single woman. She holds a temporary position at work, which makes her nervous that she might get fired. She is generally servile and timid. Considering her current state, she does not want to be single. One day, 17-year-old Ban Ha-Ni (Lee Re) from the past comes to 37-year-old Ban Ha-Ni. 17-year-old Ban Ha-Ni is totally different from her older self. The younger Ban Ha-Ni is bright and optimistic.
A time travel story between a genius engineer Han Tae-Sool (Cho Seung-Woo) and his savior from the future Kang Seo-Hae (Park Shin-Hye).
Han Tae-Sool is a genius engineer and the co-founder of Quantum and Time Company. He is handsome and he produces innovative results. Thanks to his efforts, Quantum and Time has become a world-class enterprise. He is known as a miracle worker and a hero in Korea, but reality is a little different. After his older brother's death 10 years ago, he has exhibited eccentric behavior. The company's stock price has fluctuated accordingly. One day, Han Tae-Sool learns of an unreliable truth behind his brother's death. His dangerous journey begins.
Kang Seo-Hae is an elite warrior. She can take down the biggest men with just her bare hands. She is also a sharpshooter and able to make bombs. She learned these skills to survive in a world that is dominated by gangsters and military cliques. One day, after a long and dangerous journey, she comes to Han Tae-Sool to save him.
At the age of 8, Park Joo-Hyeong went to Italy after he was adopted. He is now an adult and has the name of Vincenzo Casano (Song Joong-Ki). He is a lawyer, who works for the Mafia as a consigliere. Because of a war between mafia groups, he flees to South Korea. In South Korea, he gets involved with Lawyer Hong Cha-Young (Jeon Yeo-Bin). She is the type of attorney who will do anything to win a case. Vincenzo Casano falls in love with her. He also achieves social justice by his own way.
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