In a dystopian future marked by chaos from the depletion of natural resources, society is divided into the "Rusties," who represent the old world, and a new generation under radical transformations. To preserve humanity, scientists devise genetically modified orchids as an energy source and a surgical procedure aimed at eliminating imperfections among the population. This procedure, performed on individuals labeled as "Uglies" at the age of 16, is intended to create a uniform society, where differences are eradicated, leading to the so-called "Pretties."
Tally, portrayed by Joey King, alongside her best friend Peris, played by Chase Stokes, have shared a bond through their childhood scars, vowing to keep them even after their anticipated transformations. However, as the day of their procedures approaches, Peris, being older by three months, undergoes his surgery first and disappears into the life of the Pretties, leaving Tally feeling abandoned and anxious. Despite her many attempts to connect with him, Tally receives no response, raising her concerns about his new identity and changes.
Determined to uncover the truth, Tally sneaks into the city but is taken aback by Peris's new persona devoid of the scar they cherished. When she is discovered, the Wardens pursue her back, but she narrowly escapes thanks to a fellow student. Soon after, Tally encounters Shay, a rebellious Ugly played by Brianne Tju, who introduces her to the concept of "The Smoke"—a sanctuary of freedom that honors nature.
As they share the same birthday, Shay bonds with Tally and teaches her the exhilarating art of hover-boarding. She urges Tally to reject the surgery, highlighting the possibility of joining The Smoke and meeting its leader, David, portrayed by Keith Powers. Shay shares details of an expedient journey to this safe haven four days away, instilling within Tally a sense of adventure, although she initially clings to the desire to become Pretty.
On the eve of her 16th birthday, Tally finds herself confronted with a difficult choice when Dr. Cable, played by Laverne Cox, threatens her with a delay in her procedure until she reveals Shay's whereabouts. Tally, caught in a web of deceit and loyalty, is forced to make desperate decisions. She ultimately becomes a spy for the authorities but feels torn as she journeys deeper into the mystery of The Smoke, leading to heart-pounding revelations.
As Tally reconnects with Shay and David, she learns shocking truths about the surgeries, which dumb down the populace, allowing for easier manipulation by the authorities. David's mission—a rebellion against the toxic orchid power sources—unfolds dramatically as they forge their own path against a background of raging infernos set intentionally to obliterate the orchids.
In an intense moment, when Shay needs rescuing, Tally demonstrates her loyalty and courage despite potential threats. As their mission intensifies, Tally finds herself entwined between the chaos of her former life and the urgent call for freedom that David represents.
With twists and perilous encounters unfolding, Tally ultimately resolves to undergo a surgery meant to test a cure against the brain-dulling effects of the original procedure, swearing to remain true to her mission for justice, creating an emotional farewell to David and her friends. Despite transforming into a Pretty, Tally holds onto her childhood scar, suggesting a lingering connection to her past and the rebels' cause, thus encapsulating her internal struggle and defiance against the society that altered her fate.
