In the midst of adjusting to their new suburban life, 14-year-old Amelia "Milly" Michaelson (Lucy Deakins) struggles to cope with the emotional weight of her father's passing. While navigating high school challenges and bonding with her new friend Geneva, her 8-year-old brother Louis (Fred Savage) wrestles with bullying and academic pressure. Their mother, Charlene (Bonnie Bedelia), is further burdened by a demotion at work and her battles with computer technology.
As the Michaelson family tries to settle in, they meet their neighbor Eric Gibb (Jay Underwood), a boy with autism who lives with his uncle Hugo (Fred Gwynne). Eric's eccentric behavior and fascination with flight cast a mysterious shadow over his character, with whispers of his troubled past – including the tragic loss of his parents in an airplane accident and his uncle's indulgence in reckless drinking.
One harrowing evening, Milly and her family bear witness to a shocking sight: Eric, detained in a straitjacket by two men, is taken away. Gradually, the truths surrounding Eric's precarious situation begin to emerge, and Mrs. Sherman (Colleen Dewhurst) enlists Milly to watch over her vulnerable neighbor.
As the school year unfolds, Milly makes it her mission to connect with Eric, cataloging his fragile progress, which consists of fleeting smiles and moments of understanding. Each tiny victory offers a glimmer of hope. The turning point comes when a stray baseball hurtles toward Milly, only for Eric to miraculously appear and snatch it from midair, blurring the lines between reality and dreams.
Milly’s world becomes increasingly surreal as strange occurrences unfold – Eric's uncanny teleportations and their unusual glimpses into one another's lives leave her questioning her sanity. During a school trip, Milly tumbles off a bridge, pursuing a coveted rose. In her unconscious state, she awakens in a hospital room where Eric silently keeps vigil by the window. Their unspoken connection leads Milly to an epiphany: she believes Eric can defy gravity. Supporting her theory, Eric presents the very rose she sought and, with tenderness, draws her out of the window into the sky. Together, they ascend above the clouds, surrounded by a breathtaking fireworks display. However, the bliss is transient, yielding to the harsh reality of witnessing her father's lifeless body in the hospital.
Troubled by her fantastical claims of Eric’s extraordinary abilities, Milly confesses her experiences to her mother. Yet Dr. Grenader, a pragmatic psychiatrist, attributes her fantastical thinking to the emotional toll from her father's death – a battle he fought quietly with cancer before choosing to leave the world in an untimely manner.
Upon returning home, Milly's fixation with the rose on her windowsill deepens her conviction that Eric's powers are not mere fabrications. When she inquires about Eric's whereabouts, Uncle Hugo reveals that he has been taken away, adding to Milly's frustration. Despite their attempts, they are denied access to Eric, all while Louis faces escalating challenges from bullies and the harrowing loss of his beloved dog, Max.
As a storm rages on one fateful night, Milly glances outside only to find Eric on his rooftop, soaked and shivering. Enveloping him in a blanket, he produces a small box containing a ring, signifying their deepening bond.
The next day, as authorities approach Eric’s home, Milly takes courageous initiative, orchestrating a daring escape that culminates in an audacious chase. They reach the school rooftop, where carnival festivities create a backdrop of merriment. Amidst the cacophony, Eric turns to Milly and, with a barely audible voice, confirms that he can indeed defy gravity. Together they leap from the rooftop, only to find themselves gliding through the air, captivating the astonished crowd below, who can only watch in awe.
As Eric's departure looms, he brings Milly to her window, pouring out his love before sharing one last kiss and disappearing into nothingness. This leaves Milly transformed yet profoundly affected by his absence. In the ensuing weeks, the neighborhood is inundated with curious onlookers and scientists eager to uncover the secrets of Eric's extraordinary existence.
However, amidst the turmoil, those intertwined in Eric's story undergo inspiring changes. Uncle Hugo tackles his addiction, setting himself on a new professional path; Max rebounds from his accident; Louis finds the courage to fend off bullies using, of all things, a water gun filled with urine; Charlene embraces her tech-related challenges; and Milly regains her balance and direction, fueled by the memory of Eric. As the sun sinks beneath the horizon on the film's concluding day, Milly gazes wistfully from her window, longing for Eric’s return. In a gesture of hope, she sends a paper airplane soaring into the sky, its flight a symbol of unbounded possibilities.
