The legend of Liang Shanbo and Zhu Yingtai is set in the Eastern Jin Dynasty.
Zhu Yingtai is a beautiful and intelligent young woman, the ninth child and only daughter of the wealthy noble Zhu family of Shangyu, Zhejiang. Breaking traditions that restricted females from going to school, she convinces her father to allow her to disguise herself as a young man and travels to Hangzhou to attend classes. During her journey, she meets Liang Shanbo, a scholar from Kuaiji (now known as Shaoxing), who lives in the same province as her. They chat and feel a strong affinity for each other at their first meeting. Hence, they gather some soil as incense and take the oath of fratenity in the pavilion of a thatched bridge.
For the next three years in school, they share the same room where there is only one bed and two quilts. Zhu Yingtai falls in love with Liang Shanbo gradually. Although Liang equals Zhu in their studies, he is still a bookworm and fails to notice the feminine characteristics exhibited by his classmate.
One day, Zhu Yingtai receives a letter from her father, asking her to return home as soon as possible. Zhu Yingtai has no choice but to pack her belongings immediately and bid Liang Shanbo farewell. However, in her heart, she has already confessed her love for Liang Shanbo and is determined to be with him for all eternity. Before her departure, she reveals her true identity to the headmaster's wife and requests her to hand over a jade pendant to Liang Shanbo as a betrothal gift.
Liang Shanbo accompanies his "sworn brother" for 18 miles to see her off. During the journey, Zhu Yingtai hints to Liang Shanbo that she is actually a woman. For example, she compares them to a pair of mandarin ducks (symbolic of lovers in Chinese culture) but Liang does not catch her hints and does not have even the slightest suspicion that his companion is a woman in disguise. Zhu Yingtai finally comes up with an idea and tells Liang that she will act as a matchmaker for him and her sister. Before they part, Zhu reminds Liang to visit her residence later so he can propose to marry her "sister". Liang and Zhu reluctantly part ways at the pavilion where they first met.
Months later, when Liang Shanbo visits Zhu Yingtai, he discovers that she is actually a woman. They are devoted to and passionate about each other and they make a vow of "till death do us part". The joy of their reunion is short-lived as Zhu's parents have already arranged for her to marry a man from a rich family called Ma Wencai. Liang Shanbo is heartbroken when he hears the news and his health gradually deteriorates until he becomes critically ill. He dies in office later as a county magistrate.
On the day of Ma Wencai and Zhu Yingtai's marriage, mysterious whirlwinds prevent the wedding procession from escorting the bride beyond Liang Shanbo's grave, which lies along the journey. Zhu Yingtai leaves the procession to pay her respects to Liang Shanbo. She descends in bitter despair and begs for the grave to open up. Suddenly, the grave opens with a clap of thunder. Without further hesitation, Zhu Yingtai throws herself into the grave to join Liang Shanbo. Their spirits turn into a pair of beautiful butterflies and emerge from the grave. They fly together as a pair and are never to be separated again.
