Nathan Ellis, a 9-year-old maths prodigy, Asa Butterfield has just lost his father in a car accident. He is soon diagnosed as being on the autism spectrum, and while he values his mother, Julie Ellis, Sally Hawkins, he keeps physical contact to a minimum, treating her more as a caregiver than a parent. To keep him focused on his studies, Julie enrolls him in advanced classes at a new school filmed at High Storrs School in Sheffield, United Kingdom. There, he comes under the tutelage of a maths genius, Martin Humphreys, who has multiple sclerosis. Rafe Spall portrays a mentor who sees himself in Nathan—once a rising mind in mathematics who gave it all up when illness struck.
Seven years later, Martin Humphreys is guiding Nathan toward a spot in the International Mathematical Olympiad, a prestigious high school competition that gathers the world’s best young mathematicians. This year the Olympiad is set to be held in Cambridge after a two-week maths camp in Taiwan, where the contestants study for the test that could determine the winners. Nathan fears he may not qualify, yet he earns the chance to accompany 15 other British teenagers to Taiwan.
Armed with talent but unsettled by new surroundings, Nathan discovers he is no longer the sole smartest mind in the room, and his social anxieties threaten to derail his performance. He struggles with social cues and recoils from close contact, but he forms a bond with a female Chinese student, Zhang Mei, who slowly helps him adapt and face his fears. Through her support, Nathan and Zhang just barely make the cut to compete in Cambridge.
Back in England, Zhang stays with Nathan and his mother, who is surprised to see his behavior transform into something far more normal. Julie begins to wonder if Nathan might have feelings for Zhang, though he himself is unsure how to express such emotions. The trio travels to Cambridge and settles in for the Olympiad, while Zhang’s presence continues to shape Nathan’s experience in unexpected ways.
Things take a turn when Zhang’s uncle discovers her in Nathan’s room one morning, causing Zhang to withdraw from the competition and leave. Nathan, who believes he loves Zhang, feels torn between his growing emotions and the Olympiad itself. When he sits down among hundreds of competitors for the exam, the opening question stirs memories of his late father and the ache of losing Zhang, creating a powerful emotional overload that tests his resolve.
Nathan rushes out of the exam hall, with Martin and Julie following closely. In a quiet cafe, he opens up about the heaviness of his loss and the ache of the girl who understood him, and the three share a quiet, hopeful moment. They embrace, and Julie drives Nathan to the station to retrieve Zhang Mei, signaling a hopeful return to balance as he faces the next steps in his remarkable journey.
