Greg Wittle, played by Owen Wilson, finds himself in a monotonous routine filled with daydreams and artistic sketches during his work hours. After a life-altering event leads to his dismissal from the job, he experiences a series of vivid hallucinations wherein he imagines taking drastic actions against his boss, Bjorn, portrayed by Steve Zissis. Greg envisions hiding Bjorn's body behind the office curtains, only to escape to a bar nearby for solace.
In this bar, he encounters Isabel, a captivating yet homeless woman who seems to possess knowledge of his actions. Isabel reveals her ability to manipulate their surroundings, suggesting that they have both created this world and its consequences. She advises Greg to evade the police and sever ties with his family for safety. As fate would have it, she takes a radical step by selling his personal belongings, further entrenching him in this alternate existence.
Isabel leads Greg to a secure area akin to a homeless shelter where she showcases her peculiar tricks, such as igniting and extinguishing candles from a distance. Intrigued, Greg shares his artistic creations with her, and she entices him with crushed yellow crystals that she claims can enhance his abilities, allowing him to manipulate reality through telekinesis.
As Greg delves deeper into this world of hallucination, he finds himself losing track of time and stability, leading to a chaotic encounter at a roller rink. There, he and Isabel concoct a scheme to embarrass a local bully using their newfound powers, but the situation spirals out of control, culminating in Greg's arrest. He is eventually released, only to be pursued by his daughter, Emily, who is desperately searching for him.
During his time with Isabel, Greg's descent into madness continues as he wakes one day to find her absent, yet he discovers drawings adorning the tent—remnants of his imagination. In a fleeting moment of hope, he locates Emily's phone number and attempts to reach her, but only encounters silence. Upon returning, he faces Isabel's wrath for his communication with Emily, who she insists is merely an illusion. This leads Isabel to propose a dangerous escape plan to prove the nature of their reality, which involves utilizing blue crystals.
In a surreal twist, Greg finds himself emerging from what seems to be a collective simulation designed by Isabel, intended to explore alternate realities and their effects on the human psyche. She confesses their relationship within this simulated world and guides him through a bizarre series of revelations, explaining how the breakdown of societal issues through synthetic biology and advanced technology has allowed humanity to blossom.
As events unfold, Greg grows hesitant about re-entering the simulation. Isabel urges him to aid her in presenting her findings to the scientific community. At a gala celebrating their Brain Box, he has a poignant encounter with a ghostly manifestation of Emily, pleading for him to return to her, forcing Greg to grapple with the ultimate choice between the two disparate realms he inhabits.
As tensions escalate, Isabel's actions lead to further complications, bringing them to a desperate situation in the simulation where only one crystal remains for escape. Greg ultimately insists that Isabel flee while he confronts the consequences of his actions alone. This moment of sacrifice solidifies his belief in the reality of his daughter. Eventually, he finds his way back to Emily, rekindling their precious relationship amidst the surreal backdrop of all that has transpired.
