Mama's Affair follows Yu Mei-fung (Teresa Mo) who was once a top artiste manager. When she got pregnant, she chose family over career. Today, her 17-year-old son, Jonathan (Jer Lau), is about to study abroad, and the gap between her and her husband is growing wider. All alone, she decides to get back to the workforce. Then she meets Fong Ching (Keung To), a waiter who is passionate about singing and dancing. He reignites her spark. Yet, this causes rivalry between Jonathan and Ching...