Lin Li () leads a relatively successful and peaceful life, as most 40 year-old woman would. She is an assistant creative director at a cosmetic company and has a 14 year-old daughter with her husband and first love Chen Shi (). Things at work start to change when the company hires a popular online influencer Wen Yu () as her peer. She discovers Chen Shi is having an affair with his employee and at the same time she is diagnosed with cancer. Just as everything is looking daunting, a chance encounter with an eight year-old boy 15 years ago is about to change Lin Li's life. Dong Sheng () reappears in her life as Wen Yu's aimless 22 year-old brother with a hopeless affection for Lin Li. Together the unlikely pair helps each other through difficult times and gives each other hope and support. But can they withstand the prejudice of society and persevere with 18 years of age gap between them? Can 40 really see a new beginning for Lin Li?
