Kim Seo-Jin is a man who is driven only to achieve success in his life. Thanks to his efforts, he is the youngest executive at his company. His life is perfect, with his beautiful violinist wife Kang Hyun-Chae and a daughter. His wonderful life comes to a halt when his young daughter is kidnapped. He falls deep into despair. To change the past, when his daughter was kidnapped, he contacts Han Ae-Ri approximately one month in the past.
Han Ae-Ri has busy days with her studies and working a part-time job to make enough money to pay for her sick mother's operation. One day, her mother suddenly goes missing. Han Ae-Ri falls into despair, when Kim Seo-Jin from the future contacts her.
Ae Ri, a struggling part-timer supporting her ailing mother, faces turmoil when her mother foregoes a long-awaited heart transplant and mysteriously disappears. Amid the chaos, Ae Ri receives a call from Seo Jin, a man claiming to be from 31 days in the future, pleading for her help.
Seo Jin, once a successful construction company director, is shattered by his daughter's kidnapping and his wife's suicide. Desperate to undo his losses, he strikes a deal to restore everything—with Ae Ri's help—calling her at precisely 10:33.