"Ngày Xưa Có Một Chuyện Tình" revolves around the intertwined friendship and love story of two boys and a girl from childhood to adulthood, as they face the challenges of fate. Spanning four stages from 1987 to 2000, the three friends—Vinh, Miền, and Phúc—grow up together, experiencing the innocence of love, life's struggles, and personal growth along the way.

In a quaint village nestled in the West Vietnam, Mr. Sau Seu, a karaoke cafe owner, resides alone, eagerly awaiting his son Ut Tung’s return from Saigon for a visit. However, his hopes are shattered when he discovers he has a grave illness. To fulfill his promise to his late wife, he decides to “marry his son off.” However, this plan takes an unexpected turn when he learns that Tung has a shocking secret and is concealing it. Amidst conflicts, misunderstandings, and attempts at reconciliation, father and son gradually gain a deeper understanding of each other. Ultimately, they find happiness and peace in their own unique marriages.