The mysterious Doctor Voyan has developed a new experiment where he rewards couples with five million dollars if they stay inside an immaculate room for fifty days. If one of them leaves, the prize drops to one million dollars. There is no contact with the outside world and no entertainment, only each other's company.
However, they can get "treats" by paying for them with part of the prize money. Today's couple is Mike and Kate, who think it will be easy money. Mike thinks they've been very lucky to find this place, and Kate sees it as the second chance they deserve.
However she also points out that maybe they should split the money to make things easier. Her plan is to invest the money, which Mike thinks is incredibly boring, he sees his future as partying and having a good time without having to think about money ever again. After hearing the AI voice remind them of the rules, they explore the area and notice they weren't joking when they called it "immaculate".
Everything is white, and the only objects there are a bed and a bench. There's also a simple bathroom, which rules say they can enter one at a time; a red button they can use if they want to leave, a touch screen where they can request treats, and a big clock above the exit door that counts down the time they have left in the experiment. Their meals are designed to cover their daily nutritional requirements and are just flavorless white shake that comes in a white carton.
The room also comes with automatic lights that change throughout the day to announce morning, afternoon, evening, and when night falls, which is a sign they must take to go to bed. The touch screen allows them to set up an alarm clock, and while Mike plans to treat this as a vacation and sleep late, Kate sets up an early alarm so she can have some sense of routine. When they go to bed on their first night, Mike tries to get busy with Kate, but she's worried that they may be watched by the professor.
Since Mike insists, they end up doing it quietly under the covers. When morning comes, Kate goes to the bathroom to look at herself in the mirror and recite a few words of affirmation to keep her spirits up and her goals fresh. After they both shower, they throw their clothes into the bathroom's laundry chute, and in exchange, they receive very plain pajamas, although at least these have some color.
To keep themselves busy, Kate tries to theorize why Voyan is running this experiment, so Mike tells her about the documentary he saw about this guy's previous experiment that ended with a blue-collar family in tragedy. Nobody knows why Voyan did all this, they only know he's got tons of money and he like using it to put people in unique circumstances because he's intrigued by the human condition. Keeping themselves entertained becomes a problem sooner than they expect.
Kate likes to meditate while Mike stares at the clock sometimes, he also goes on philosophical tangents about various subjects like the meaning of the color white, which he analyzes with all his art school knowledge, or the direction in which they should be brushing their teeth. Kate always reminds him not to stare at the clock and to keep his mind on the prize, but it's hard to think positively when Mike can't even sleep well. Kate keeps up her routine of affirmation words and making the bed, she also tries to keep Mike's spirit up.
When Kate meditates, Mike tries exercising, mainly by running. Together, they play hand-clapping games, Marco Polo, or even dance. Whenever they take off their dirty pajamas, they're given another pair that looks exactly the same.
A few weeks have passed when something different finally happens: Mike finds a bug that has sneaked inside the room. After baby-talking to it, Mike tries to feed it some of the meal shake, but as soon as he pours some drops on the floor, the AI voice reminds them that food can only be used for consumption by the contestants. Worried about the bug not surviving in here, Mike requests some way of letting the little guy out, promising he doesn't want to leave.
Kate explains to him that the speaker through which the AI voice comes out doesn't seem to be two-way, she's already tried, making Mike decides he's going to push the button to open the door. This starts an argument because Kate is sure pushing the button will make them lose even if Mike doesn't actually leave and only puts his hand out for a stupid bug. After putting the insect down, Mike tells Kate the bug is a living being and that she has no compassion, so Kate accuses him of being condescending because she isn't vegan like him.
As the argument gets louder, Kate finally confesses she thinks Mike is only vegan because he wants to piss off his well-off dad who have Mike everything he needed, therefore he never suffered and now he wants to have artsy street art cred. Then, Kate tries to walk away from this conversation, but she ends up stepping on the bug, and Mike has trouble believing her when she says it was an accident and apologizes. Mike spends the rest of his day sulking in a corner until he finally decides he's had enough, doing nothing it's just not healthy.
Since each of them can take two treats, Mike is going to ask for one even if takes out one hundred thousand dollars off their prize. Kate doesn't approve, but Mike doesn't need her permission, and his treat ends up being a single green crayon. It's not much, but at least now Mike can do his art on the walls.
After watching him draw for a while, Kate asks him to draw her, and Mike accepts. However, he refuses to de realistic portraits because they're boring, he prefers to stick to his style, causing Kate not to want to model for him anymore. Mike draws until there's no more crayon left, pissing Kate off when he leaves green stains all over the bathroom and the towel on the floor.
Later, Kate apologizes for having behaved like a twat and explains this is harder than she thought, but at least they only have twenty days left. Days continue to pass in boredom until one morning, Kate wakes up to find a gun in the bathroom. They're too scared to check if it's loaded and its presence is haunting, so they decide to hide it under the bed because the AI forbids them to put objects that aren't clothes inside the laundry chute.
Sometime later, the couple is finally rewarded with connect time, which will play for them messages sent by their loved ones. Mike gets a message from his sister, who tells him how she and their parents are doing, but she also thinks Mike isn't dating Kate anymore. Seeing his sister makes Mike very happy, but Kate doesn't want a connection of her own and panics when the screen puts a video of her dad, who is finally off the streets and living in a homeless shelter.
Since the video won't stop no matter how much she asks, Kate runs to hide behind the bathroom entrance and cry, and Mike comes over to comfort her. After sleeping by clinging desperately to her boyfriend, Kate doesn't get up when the alarm announces the morning and stays in bed all day because she's fallen into a depressed state. When Mike expresses his worries, Kate tells him she hadn't seen her father in years and always lied to Mike about who he was because she was ashamed of her dad and the way he drank away the house, her school fees, and her chances of growing up like a normal person.
With only a little over two weeks to go, Kate still stays in bed while Mike tries to find new ways to entertain himself, like modifying his drawings by smudging the crayon with his fingers or reading the pajama label in as many emotions as possible like those acting exercises. He tries to make Kate eat by making some jokes about the food, but it's pointless, so he ends up joining her in bed in hopes he can comfort her. It still doesn't work, and Mike sometimes decides to sleep on the floor just to feel something different.
One morning, he tries to convince Kate to take a treat, but she refuses to lose that money. Growing increasingly frustrated, Mike mentions he isn't sure he can do this anymore, and that finally inspires Kate to get out of bed. Before she takes a shower though, she tells Mike to take his second treat, even if costs a quarter million.
Mike does so and is shocked to see the door open to allow a naked woman called Simone enter the room. She doesn't know anything about the project, she's just an actress getting paid for a gig that required signing lots of NDAs and while she was booked for a month, her agent said she's probably staying for twenty-four hours. Kate doesn't like her presence very much and makes Mike give her his t-shirt so Simone can cover up at least a bit.
Simone notices Mike's art and praises it, even recognizing the influences, which pisses Kate off more. When night falls, Mike offers to sleep on the floor while the girls take the bed and Simone offers to stay awake while they sleep. Kate is annoyed by their attempt at manners and decides they can all share the bed as long as she sleeps in the middle.
That night, it's Kate the one to have trouble sleeping. In the morning, Kate doesn't find Simone on the bed and thinks she's gone, but actually, she's in the bathroom. Not being able to take it anymore, Kate decides to take a treat and receives a little box with three fun candies.
Kate immediately takes one and offers one to Simone, but Mike only accepts one too after lots of hesitation. The three of them begin dancing and flailing around the room, they also share a few group kisses. However, after a while, Mike begins going through a bad trip, seeing blood everywhere and dreaming he's underwater while seeing his younger brother fall with him.
The women bring Mike back to reality, but he's still panicking and asking to leave while mentioning something about Shawn and drowning. Kate has to drag him back to bed and comfort him until he's asleep. Afterward, Simone asks what Mike had been talking about, and Kate tells her Mike's little brother Shawn drowned in the family's pool while Mike was supposed to babysit him, which makes him feel guilty still to this day.
Mike had been high when it happened, which adds to the injury and explains why he had been hesitant to accept the candy here. Simeone also asks how they met, and Kate remembers fondly how on a rainy day, she had no umbrella and Mike came to her, offering to catch all the raindrops so she wouldn't get wet. When Mike finally wakes up, Simone shares that she lost her mother when she was a kid, and the two of them bond over grief and lost loved ones.
Simone takes Mike's hand to comfort him and when Kate sees them, she freaks out, thinking Simone wants to steal her boyfriend. Simone calls her attitude out, pointing out that Kate lashes out because she's actually an insecure person, which starts an argument. Mike yells at them to stop before walking away, thus Kate tries to apologize, admitting it was probably nothing that she saw, yet Simone fans the flames by saying maybe it wasn't.
The following morning, Mike isn't feeling well, but Kate is concentrated on other things. Simone is finally gone, but there's also a message from her on the wall on green crayon thanking Mike for a wild night. Kate freaks out, not listening to Mike when he explains he didn't do anything and this is like the gun, something the room is doing to mess with them.
In her anger, Kate pushes Mike to the floor, making him hurt his head and bleed. Mike steps away from her, reminding her that he's never cheated on her even when she moved to New York, he also stopped seeing his so-called rich friends not to make her uncomfortable and didn't finish college to stay at home with her when she was depressed; yet all he gets in return is jealousy. Crying, Kate continues to apologize, but their conversation is interrupted when Mike begins feeling dizzy from the wound.
He truly thinks he needs a doctor, but Kate brings him some of the meal shake so he can put some sugar in his system and covers his wound with a towel, reminding Mike that the contract said they don't have allowance for medical intervention. Mike can't believe what he's hearing, and he starts wondering if Kate really cares. His wound turns out to be small and it eventually stops bleeding, but he is scared of how far she would've gone if it had been worse, perhaps she would've let him bleed for money.
Hating what this place has done to them and realizing money isn't going to fix how broken they actually are, Mike decides to leave, inviting Kate to do the same. Kate refuses though, pointing out it's easy for him to talk like this because he's always had money, and she even retrieves the gun to threaten him into staying. However, Mike ignores her and presses the button, finally leaving the room only a few days before victory.
After lots of laying around and freaking out in the shower, Kate sees the raindrop drawing on the wall, inspiring her to approach the button too and consider her options with only two days left. Many months later, a now single Mike is going for a run when he sees Kate coming out of a building. They haven't seen each other since the room and decide to go for a walk to chat and catch up, but when Mike asks Kate if she left the room or won, she dodges the question.
At least though, she offers an apology for what happened. As they walk away, the building is revealed to be the homeless shelter, which has a plaque saying an anonymous donation allowed them to build the new kitchen. Meanwhile, in the immaculate room, a new couple arrives to take the challenge.