Her hybrid causing chaos is pure shock

- Elisabeth Sparkle, a TV aerobics star, is fired on her 50th birthday and gets into a car accident.
- At the hospital, a nurse gives her a flash drive with "The Substance," a serum that creates a younger version of the user.
- Elisabeth orders the serum and "births" a younger self named Sue from her back.
- They must switch bodies every seven days, with one resting while the other lives.
- Sue quickly gains fame, but Elisabeth struggles with envy and low self-esteem.
- Sue neglects the switching schedule, leading to Elisabeth's rapid aging.
- Sue extracts enough serum to last three months but runs out before a New Year's Eve special.
- Elisabeth decides to terminate Sue but regrets it and switches with Sue again, who then kills Elisabeth.
- Sue's body deteriorates without Elisabeth.
- In a desperate attempt to save herself, Sue uses the remnants of the original serum, creating a monstrous hybrid.
- The monster shocks the public during a live broadcast, causing chaos.
- The monster escapes but eventually explodes.
- Elisabeth's face emerges from the remains, crawls to her star on the Hollywood Walk of Fame, and merges with it.
- The next day, her remains are cleaned up.