Billy Shine is a former Broadway dancer and singer who has not left his Los Angeles apartment in nearly a decade due to severe agoraphobia, a condition marked by intense fear of leaving safe environments. He survives on a modest monthly allowance from his wealthy parents, has his groceries delivered, and tips the delivery men to take out his trash. He sleeps fitfully, haunted by a recurring dream of enormous white wings that intensify when he is distressed.
One evening, Billy notices nine-year-old Grace Ferguson sitting alone on the front stoop of their apartment building as darkness approaches. Her hair is matted and her sweater misbuttoned. Billy forces himself onto his first-floor patio for the first time in years, crawling on his belly to the railing. Grace asks why he is crawling, and they strike up an exchange. Billy learns she has a key to her basement apartment but refuses to go inside. When he returns the next evening to ask why, Grace explains that if she sits inside, nobody will know she is in trouble. She asks Billy for help, but he replies that he cannot even help himself.
Grace lives with her mother, Eileen Ferguson, who has a drug addiction and has relapsed. At a Saturday-night Narcotics Anonymous (NA) meeting, Grace learns her mother is using again. Eileen's NA sponsor, Yolanda, quietly slips Grace her phone number "just in case."
Mrs. Hinman, the elderly attic tenant, questions why Grace is outside alone. Rayleen Johnson, the manicurist across the hall from Billy, argues against calling Child Protective Services, insisting foster care would be worse and speaking from personal experience with the system. Felipe Alvarez and Jake Lafferty, upstairs neighbors, clash on the sidewalk over Grace; Lafferty calls Felipe "Jose" despite repeated correction. Grace steps between them and reveals that her mother will not wake up.
A caregiving network forms. When a county social worker calls, Rayleen impulsively lies, claiming to be Grace's paid babysitter. At Grace's persistent suggestion, Rayleen brings the girl to Billy's door. Billy agrees to watch Grace for two hours each afternoon. Grace hugs him, and he marvels at the sensation of human touch after more than a decade of isolation. Lafferty comes to Billy's door and demands to know if Billy is gay, citing anti-gay stereotypes about child safety. Billy refutes the claim. Despite this hostility, Lafferty is consistently kind to Grace. He delivers a sheet of plywood for a dance floor and anonymously buys her first real tap shoes.
Billy teaches Grace the time step, tap dance's foundational move, using his childhood shoes padded with socks. Felipe teaches her basic Spanish on walks home from school. Rayleen takes her to the salon for a badly needed haircut. Lafferty tells Grace her caregivers are "enabling" Eileen, shielding her from consequences that might motivate her to get clean. Billy reluctantly agrees. Days later, a gunshot is heard. The building superintendent confirms that Lafferty has died by suicide. Grace reflects that he did three kind things for her: the dance floor, the tap shoes, and telling them the truth.
Grace proposes they refuse to let Eileen see her until Eileen gets clean. When Eileen finally wakes and searches frantically for Grace, Grace hides at Billy's, crying for over an hour. The group holds firm. Grace meets Peter Lafferty, Jake's estranged son, who reveals he recently cut off contact with his father. Grace realizes Lafferty's isolation contributed to his death, solidifying her belief that nobody should be alone. She discovers Lafferty had a secret cat and names it Mr. Lafferty the Cat. When Eileen grabs Grace and drags her to the basement, injuring Grace's hip, Billy storms into the hallway and pounds on Eileen's door.
A new neighbor, Jesse, moves into Lafferty's old apartment. He is from Chapel Hill, North Carolina, on leave to be with his dying mother. Jesse practices reiki, a hands-on healing technique, and smudging with white sage, a ceremonial practice meant to clear negative energy. Billy recognizes a deep attraction to Jesse, but when Jesse reveals his interest in Rayleen, Billy selflessly encourages the connection. Jesse organizes a smudging ceremony in Lafferty's apartment where each neighbor speaks to Lafferty's lingering energy. In weekly meetings that follow, Grace pushes the neighbors to share why they are alone, gradually deepening the group's bonds.
Jesse accompanies Billy on morning walks to Grace's school, providing physical grounding as Billy walks farther each day. Rayleen confesses deep trust issues with men from her time in foster care. Billy tells Rayleen if he can walk to school, she can go on one date with Jesse; the two begin dating. Meanwhile, Ms. Katz, the county social worker, warns Rayleen that if Grace's living situation is not legalized within a month, Grace will enter foster care. Yolanda helps Eileen stay clean for Ms. Katz's return, but Ms. Katz announces ongoing check-ins.
Grace's school invites her to perform a tap solo at an assembly. Billy choreographs an ambitious routine, putting on his own adult tap shoes for the first time in over a decade. In the weeks before the performance, Billy dances Grace to school each morning, drawing growing audiences of neighbors. One morning he falls while waltzing and badly injures his nose and ribs. Jesse and Rayleen, returning from North Carolina where Jesse's mother has died, arrive just in time to help him recover.
On the day of the assembly, Billy, Jesse, Rayleen, Felipe, Mrs. Hinman, Eileen, and Yolanda all attend. Grace performs flawlessly: Her time step, Buffalo turns (a spinning tap move), and treble hops (a rhythmic jumping step) are perfect. She receives a standing ovation. As Billy begins to congratulate Grace, Eileen snatches her away, brandishing her thirty-day sobriety chip and threatening to have the neighbors arrested for kidnapping.
Eileen forbids all contact. Grace becomes depressed and withdraws. Grace slips a note under Billy's door asking what he was going to say at the assembly. Billy writes back that she was "the shiniest thing I've ever seen," but the reply sits uncollected for more than a month, and he eventually takes it back. Two months later, another note appears: "MR. LAFFERTY THE GIRL CAT MISSES YOU. AND SO DO I. LOVE, GRACE," bordered by hand-drawn wings. During the year of separation, Jesse and Rayleen move to North Carolina. Felipe moves in with his girlfriend, Clara. Mrs. Hinman passes away. Billy sinks into isolation.
At Eileen's one-year sobriety anniversary, Yolanda guides her through a fearless inventory of character defects. Yolanda pushes Eileen to acknowledge that isolating Grace is selfish. Eileen admits she was wrong but does not change her behavior. Yolanda tells her that words without action are meaningless. Eileen then visits Billy and awkwardly attempts an apology. Billy tells her no one could possibly feel humiliated in front of him. Minutes later, Grace bursts through Billy's door, leaps into his arms, and asks when they can dance again. Eileen has finally relented.
In the final scene, Felipe and Clara drive Billy and Grace into the desert at night so Grace can see the real stars for the first time. Billy reflects that the world was always this big; it was just waiting for him to come back. Grace asks how the stars make him feel. He says the world feels big again, and also that he feels insignificant. Grace replies that he is important to her. Billy admits he is running out of bravery and asks to go home. Grace sighs, agrees, and silently reminds herself that the stars will still be there whether she can see them or not.