The film is set in present-time United Kingdom in an alternate history. Eight candidates dress for what appears to be an employment assessment exam; they enter a room and sit down at individual desks. Each desk contains a question paper with the word "candidate", followed by a number, from one to eight. The Invigilator, a representative of the company named DATAPREV, explains that the exam is 80 minutes and consists of only one question, but there are three rules: they must not talk to the Invigilator or the armed guard at the door, spoil their paper, or leave the room. If they do, they will be disqualified.
As the exam timer starts, it turns out that the papers are blank; one Chinese candidate is immediately disqualified for spoiling her paper when she begins to write on it. The seven remaining candidates realize they can talk to each other and work together. "White", who is arrogant and rude, suggests nicknames based on physical appearance: Black, White, Brown, Blonde, Brunette, and Dark, refer to their skin and hair colours, and Deaf for one candidate who does not pay attention to the others. The candidates use the lights, bodily fluids, and fire sprinklers to reveal any questions on the paper, with no luck. It is revealed that the company in question is responsible for a miracle drug which a large part of the population are dependent upon after a viral pandemic, including Brunette's partner. White takes control of the group and causes Brunette to be disqualified by tricking her into burning her paper so the group can test the water sprinklers. He also tricks Deaf into ripping up his own paper.
White taunts the others, saying he knows the question but will not tell them. Black subdues White and ties him to a chair; White says he needs his medication, implying he has the virus, but the others do not believe him. Brown then accuses Dark of being a plant from the company, as she demonstrates much knowledge about the internal workings of the company. After Brown tortures Dark into revealing that she works for the company, White goes into convulsions, showing he has the disease. Dark asks the unseen Invigilator for help and is disqualified.
Blonde retrieves the medication for White, reviving him, and the others release him, demanding to know the question; White suggests that there is no question and that the company is going to hire the last remaining candidate. Black steals the guard's gun, but it requires the guard's fingerprint ID, giving White time to steal it. White forces Brown to leave the room at gunpoint, disqualifying him, but when he forces Blonde to leave, she turns off the voice-activated lights, allowing Black to attack White.
When the lights are turned on, Black dies from a gunshot, and Blonde is hiding in the hallway, with one foot still inside the room. Before White can kill her, the exam timer runs to zero. When White addresses the Invigilator, he is disqualified, as Deaf had earlier set the countdown forward by a few minutes. Blonde then remembers that Deaf had been using glasses and a piece of broken glass with an exam paper earlier but was ignored. Taking the abandoned glasses, she finds the phrase "Question 1." on the exam paper in minuscule writing.
Blonde realises that Question 1 refers to the only question asked of them by the Invigilator: "Any questions?" She answers, "No." The Invigilator and Deaf enter; the Invigilator reveals Deaf is actually the CEO of the company and inventor of the cure for the virus, which can also heal any wound. The bullet that hit Black contained this cure, and he awakens, healed. With the drug about to be released to the public, the company needed to hire someone who was not only able to make tough choices but is also compassionate, which Blonde had demonstrated throughout the exam. Blonde passes the exam and accepts her new job.
Who is tricked into ripping up his own paper?
Deaf