Aspiring Chinese-American writer Billi maintains a close relationship with her grandmother who lives in Changchun, China.
After receiving a rejection letter for a Guggenheim Fellowship, Billi discovers from her parents, Haiyan and Jian, that Nai Nai has been diagnosed with terminal lung cancer, and is predicted to have only a few months left to live.
Through deception and manipulation of medical test results, the diagnosis is kept secret from Nai Nai herself. Nai Nai is, instead, falsely told that her recent doctor visits are merely for benign findings. A wedding for Billi's cousin, Hao Hao, from Japan has been planned in China, as an excuse to unite the family together and spend what is expected to be one last time with Nai Nai. Fearing Billi will end up exposing the lie directly to her grandmother, Haiyan and Jian tell her to stay behind in New York City where she currently lives.
Billi disobeys her parents' orders and ends up flying to Changchun by herself, shortly after the rest of the family arrive there. Though Billi assures her parents that she won't reveal the cancer diagnosis to Nai Nai, throughout the trip Billi clashes with the rest of the family, including the doctor treating Nai Nai, over their deliberate dishonesty towards her grandmother.
Guilt-ridden, Billi expresses conflicted thoughts with her parents over the Chinese cultural beliefs that result in a family refusing to disclose such a life-threatening disease to the matriarch. One night, her uncle, Haibin, contends that the lie allows the family to bear the emotional burden of the diagnosis, rather than Nai Nai herself—a practice of collectivism that, Haibin acknowledges to Billi, differs from the individualistic values common in Western culture. Billi later learns that Nai Nai also created a similar lie to her husband when he was terminally ill up until his death.
On the day of the wedding, both Haibin and Hao Hao break down in tears on separate occasions, but manage to proceed through the rest of the banquet as planned without Nai Nai raising any suspicions. That night, Nai Nai gives Billi a hóngbāo, encouraging her to spend the money as she chooses. When Billi reveals to her grandmother about the Guggenheim Fellowship rejection, Nai Nai responds with encouragement, inspiring Billi to continue following her dreams.
Billi keeps her promise of maintaining the lie and shares a tearful goodbye with Nai Nai, as the rest of the visiting family members return to their homes in Japan and America. Shortly before the film ends, footage of director Lulu Wang's grandmother is shown, with accompanying text that reads: "Six years after her diagnosis, Nai Nai is still with us."
- Awkwafina as Billi
- Tzi Ma as Haiyan
- Diana Lin as Jian
- Zhao Shuzhen as Nai Nai
- Lu Hong as Little Nai Nai
- Jiang Yongbo as Haibin