Myeong-jun accepts his ex-wife Hye-eun's proposal to kidnap an 11-year-old girl named Ro-hee to pay for his daughter's hospital bills. En route to execute his plan, someone collapses before his car, which turns out to be Ro-hee. He takes her home, but she can't remember anything when she wakes up. Myeong-jun claims to be her dad and contacts her parents for the ransom, but they can't be reached.

Myeong-jun finds out that Ro-hee's parents have been murdered. He can no longer demand ransom or bring Ro-hee back to her home. As he heads to Ro-hee's home, a suspicious figure approaches Ro-hee who is home alone. Meanwhile, Sang-yun, the detective in charge of the case of the murdered hospital director and his wife, learns of their daughter's kidnapping and begins tracing Myeong-jun's footsteps.

Ro-hee finds out that Myeong-jun is not her dad but a kidnapper. Myeong-jun decides to take Ro-hee to the police station and turn himself in. Right then, Ro-hee regains a part of her memory and is left in shock. Meanwhile, Sang-yun discovers something about Myeong-jun's past.

Myeong-jun and Ro-hee stay the night at Hye-eun's house, the mastermind behind the kidnapping. Ro-hee is in disbelief when she discovers Myeong-jun's decision to take all the blame for kidnapping her. Ro-hee remains suspicious of Hye-eun and, in the end, finds out the real reason for Hye-eun leaving Myeong-jun and Hee-ae. Meanwhile, Sang-yun finally faces Myeong-jun after an unyielding pursuit.

Myeong-jun and Ro-hee find themselves in Choi Jin-tae's villa. Myeong-jun learns of "The Genius Child Project," a brain experiment Ro-hee was a subject in. Dr. Mo attempts to separate Ro-hee and Myeong-jun. Meanwhile, Sang-yun digs into a case from 30 years ago to catch the culprit of the hospital director and his wife's murder case and hears an unexpected name from a witness of a past case.

Ro-hee's escape from Mo Eun-sun and Jaden is short-lived, as Jaden catches her. Myeong-jun finds himself waking up on a stowaway boat. He puts his life on the line and fights to return to Ro-Hee. Meanwhile, Sang-yun, who learns from Myeong-jun about Ro-hee's partially recovered memory, hears shocking news of a murder case while chasing Cheol-won.

Myeong-jun turns to Sang-yun for help to save Ro-hee. However, Jaden, who deems Ro-hee as a subject of the experiment and an investment opportunity, also does not give up and pursues her. Meanwhile, Sang-yun, swayed by Myeong-jun's genuine concern for the kidnapped child, places his trust in Myeong-jun to turn himself in but gets put in a tough position when he doesn't show up.

Myeong-jun and Hye-eun's complicated past unravels, and Sang-yun remains resolute in his suspicions about Hye-eun. However, Sang-yun gets suspended for failing to apprehend Myeong-jun and can no longer investigate the murder and kidnapping cases. Meanwhile, Myeong-jun hides himself in Hye-eun's house and discovers a mysterious object. Myeong-jun's suspicions about Hye-eun begin to grow.

Hye-eun aims to exchange Choi Jin-tae's research material with Jaden, and her true colors come to light. Jaden attempts to send Ro-hee overseas along with the research material. However, Ro-hee searches for ways to escape her situation. Myeong-jun, who is struggling to save Ro-hee from Jaden, turns to Sang-yun for help, who continues to pursue Myeong-jun despite being suspended.

Myeong-jun is torn between his suspicions of Hye-eun and his desire to believe in her. An alliance between the kidnapper, the kidnapped child, and the detectives in pursuit of them is formed to confront Jaden and his men. With their combined efforts, Ro-hee finally returns home, but an unexpected visitor appears.

Myeong-jun gets arrested in front of Ro-hee. Ro-hee and Sang-yun work together to prevent Myeong-jun from being falsely accused and to reveal the truth about the murder of the hospital director and his wife. Meanwhile, Hye-eun learns of Myeong-jun's arrest, finalizes her deal with Jaden, and leaves in search of freedom.