Computer game designer Brendan and his wife, Claire, are grieving for their daughter Sam, who drowned trying to retrieve her
Curious George doll from the ocean. As they reluctantly rummage through Sam's belongings, Brendan finds a copy of
The Berenstain Bears. To the bewilderment of Brendan and his brother-in-law Matt, they remember the title with "
Berenstein," even though they find no evidence that it was ever changed. This leads them to learn about many other examples of the
Mandela Effect, collectively shared "false memories". Brendan and Claire discover further discrepancies, such as clearly remembering that Sam's doll had a tail when it actually does not. Eventually, Brendan concludes that the discrepancies are due to shifts between
parallel universes and that Sam is still alive in one of them. Despite objections from Claire and Matt, he tracks down Dr. Roland Fuchs, a scientist who has been ostracized for holding similar beliefs about reality. Dr. Fuchs's research indicates that the universe is a
computer simulation, with the Mandela Effect the result of reality being rewritten to prevent its inhabitants from perceiving it as a simulation. They begin developing a special computer program that, when run on the
quantum computer at Dr. Fuchs' old campus, could interrupt the simulation. This revelation takes a toll on Brendan's mental health and marriage. He starts to have visions of Sam, which at first no one else sees, until one day she is suddenly and inexplicably alive and everyone can perceive her, though Claire soon becomes distraught, believing that Sam should not be there. Disturbed, Brendan visits Dr. Fuchs, only to be informed that he died by suicide two months previous. Having talked to him mere hours before, Brendan decides the alteration in his reality is the simulation's attempt to thwart their plan. He rushes to finish the program, sneaks into the college computer department, accidentally kills a faculty member as he threatens to call security on Brendan, who then steals his badge, enters the control room of the quantum computer, and runs his program. He then rushes home as glitches manifest and destabilize reality. His family hold each other tightly while the entire simulation crashes. The simulation restarts, recreating the history of the universe. The family is shown at the beach again, but this time Brendan asks Sam to leave her Curious George doll — now without a tail — before going to the water. This saves Sam's life and allows the simulation to continue beyond the event that originally led to its discovery and crash. ==Cast==