Kim Joon Yeong is a famous thoracic surgeon, but he isn't a very good father to his daughter Eun Jung. On his daughter's birthday, he witnesses his daughter die in an accident in front of him. From that moment, the same day begins to repeat itself, but he can't seem to stop the accident. Lee Min Cheol, who also loses his wife in an accident on that day, suddenly shows up. Everything is the same. Only the two of them change. Together, they struggle to find the secret of that day.