In the middle of the night, a woman lies in her bathtub, cutting enormous moles off her skin while talking on the phone in a frightened tone. She hears a crash and leaves the bathroom to investigate before being murdered by an unseen attacker.
Actress Samantha Lake, Elisabeth Moss, formerly relevant for a lead role in television, struggles to secure roles and date as she faces ageism and bodyshaming. Young actress Chloe Benson whom she used to babysit recognizes and greets her warmly during a casting audition. A producer urges Sam to undergo a rejuvenating procedure in Shell, a beauty company that mostly serves celebrities using genetic technology. Sam arrives at the clinic but is about to walk out on her appointment before Dr. Hubert, Arian Moayed, a scientist employed by Shell, gently and reassuringly talks her into reconsidering her choice. As she awaits to be called for the procedure, still reluctantly, Chloe spots Sam again and encourages her to carry on with it.
Sam comes out of the procedure successfully, her younger appearance giving her confidence and landing her an invitation for a Christmas party hosted by Shell’s CEO Zoe Shannon, Kate Hudson, who befriends her. Initially starstruck, Sam soon finds overly extravagant aspects of Shannon, but appreciates the new friendship all the same.
Three months later, Sam has landed a coveted role, her dating life and friendship with Zoe thrive, and she has employed her best friend Lydia, Este Haim, as her PA, who notices a tiny mole in her neck which prompts her to go back to the clinic, where Hubert removes it and calls it a minor side effect. Two detectives, Flores and Abramson, call at Sam’s new place as Chloe is missing since last Sam saw her, giving her a number to call should she learn anything. She also learns that Hubert has been fired from Shell and one night receives a call from Chloe who warns her about surveillance.
Soon Sam finds more moles on her leg and vomits black vile on a co-star and a journalist while filming. She locks herself in her camerino until Zoe arrives as she had requested and takes her to her mansion; Sam takes a chance while Zoe is in the kitchen to sneak into the bathroom and make a call. A suspicious Zoe bringing tea demands to see her call log, threatening her if news leak about the side effects; Sam throws the hot tea in Zoe’s face and escapes her driver and henchman Cornelius, saved by Lydia who had followed her and drives her to a diner to meet Flores and Abramson. Sam plays in her bracelet cellphone the conversation with Zoe, but the detectives claim that her recording is illegal and Sam realizes that they actually work for Zoe. She calls an automated taxi cab to escape them and they chase her but are hit by a truck. Sam calls at Hubert’s place and he cures her worsening skin condition; in the morning, Sam is horrified to find Chloe’s medication in the bathroom and confronts him. Hubert explains that he and Chloe were together when her own condition worsened; Sam suspects that she is in the house and finds a room where she is locked, apparently transformed into a feral creature; she comes back to find Hubert stabbed to death by Cornelius, who subdues and kidnaps her.
She wakes up in a secret part of Shell’s headquarters faced by Zoe’s lawyer Chan and lead scientist Dr. Brand, who had developed the genetic technology for the procedures and explains to Sam the possible side effects. Zoe joins them and pressures Sam to accept a deal to buy her silence; Sam refuses and demands Chloe’s liberation; a truck appears bringing Chloe transformed into a gigantic lobster before she breaks out and kills Chan and Brand. Sam hides and finds Lydia, freeing her from captivity; Cornelius intercepts them but is killed by Chloe. Both ladies hide in a lab, where Zoe follows them, confessing to have secured Sam’s recent role out of pity. Chloe appears and spares Sam; Zoe locks herself into a laboratory tube and Chloe bangs the computer which triggers the procedure that spirals out of control, killing her as Sam watches.
Some time later, Sam has published a book denouncing Shell’s actions, despite the company still operating and thriving. Her career receives renewed attention and she is happy with her social life, including her friendship with Lydia.
