As a hardworking scriptwriter, So-hye (Kim Hyun-joo) is writing a drama about cancer when coincidentally she is diagnosed with breast cancer and learns she has five months left to live. She decides to live it up, leave no regrets, and do whatever she feels like doing. However, as a workaholic, she also commits to finishing her last project, then plans to leave quietly. But Hae-sung (Joo Sang-wook), a famous star, and her first love, suddenly shows up and her plans fall through. So-hye is actively opposed to casting Hae-sung as the lead in her latest drama. His stiff, robotic acting and constant nagging annoy her, and they occasionally have petty fights. But along the way, they actually seem to be falling in love. Meanwhile, Jun-gi (Kim Tae-hoon) has been by her side, both as her doctor and a friend. He knows So-hye's bright demeanor sometimes acts as a cover for her secret burden. He knows her well, and he's been through it himself. Though he can't cure her, he wants to be her steady soulmate, and face the reality together. Jun-gi and Hae-sung fight for So-hye's love, and with mixed emotions, she is indecisive. How can she decide when she only has a few months left? What is the best way to leave without regrets?