Struggling actor Simon Williams is fired from a small role in the series American Horror Story after delaying production by overthinking his character and making repeated requests for changes. He is dumped by his girlfriend Vivian the same day. Simon meets actor Trevor Slattery, known for playing the "Mandarin" as part of a terrorist plot, who informs Simon that he is auditioning for acclaimed director Von Kovak's remake of the 1980s superhero film Wonder Man. As Wonder Man was one of his favourite childhood movies, Simon begs his agent Janelle Jackson for a chance to audition but is rejected due to his firing and behaviour. Simon gets the audition information from her computer and goes anyway. After seeing Simon panicking about how to approach the character, Slattery advises him to give a more natural performance which helps Simon in the audition. After the pair have drinks, Slattery is called by Department of Damage Control (DODC) agent P. Cleary to confirm that he has made contact with Simon, who is suspected of having superpowers and is considered unstable and dangerous.

After he was kidnapped from prison and held by Xu Wenwu's Ten Rings criminal organization, Slattery returns to Hollywood intent on living up to his mother's hopes for him as an actor. He is immediately arrested by the FBI and Cleary offers him the option of working for the DODC in exchange for not finishing his prison sentence. In the present, Janelle tells Simon that his Wonder Man audition impressed the casting director and he has been asked to do a self-tape audition for an independent film. Simon gets frustrated trying to film the audition himself, and seeing Vivian in an old self-tape video causes his powers to activate: his body releases an explosion of energy inside his apartment. Simon asks Slattery for help with the audition just as Cleary tells Slattery to use a device to hack Simon's computer. After unsuccessfully trying to film the audition at a self-tape studio, Slattery's apartment, and the house of Slattery's nemesis Joe Pantoliano, the pair return to Simon's apartment and film a successful take. Slattery secretly hacks Simon's computer and also discovers damage from the explosion.

Cleary is unable to find evidence of Simon's powers from his hacked computer. He tells Slattery that he needs to go to Simon's childhood home in Pacoima, Los Angeles, for the birthday party of Simon's mother Martha, using a wiretap to record his conversations. Slattery convinces Simon to take him and is introduced to Martha, Simon's brother Eric, and other relatives. While Martha is proud of Simon, Eric is dismissive of his career and Slattery finds that none of the other relatives are close to Simon or know much about him. Martha tells Slattery that Simon has always been lonely and she is happy that he has made a friend. Simon argues with Eric and unintentionally destroys part of the kitchen which Eric recently had renovated. Simon and Slattery leave the party, and Simon states that Slattery is the first person outside his family to know about his powers. He considers whether Eric is right and it is time for him to give up acting. Slattery decides to destroy the recording from his wiretap, just as Janelle calls to inform them that they have both been given call backs for roles in Wonder Man.

DeMarr Davis, a doorman working at the Wilcox Club in Los Angeles, is exposed to toxic waste from a Roxxon dumpster and is transported to a door-filled dimension. This gives him the ability to phase through solid matter, and for objects to teleport by passing through his body. After he saves actor Josh Gad and other club patrons during a fire, the press dubs Davis "Doorman" and Gad hires him as a bodyguard. While trying to come up with an interesting hook for his heist film Cash Grab, Gad decides to cast Davis as one of the robbers and use his powers in the film. Cash Grab is a success and Davis's celebrity grows, but overexposure and public criticisms take a toll and lead him to alcoholism. During the filming of a sequel, Cash Grab 2, Davis loses control of his abilities and Gad disappears while passing through his body. With no one able to find Gad, the DODC places Davis under lifelong surveillance and the Hollywood studios create the Doorman Clause, banning superpowered people from appearing in film and television, and requiring actors to sign contracts stating that they have no powers.

Slattery helps Simon - who is already anxious about the call back - celebrate the good news and ignores calls from Cleary. The pair are cornered by a group of drug dealers that Slattery owes money to, forcing Simon to use his powers to incapacitate them. They spot a boy who has recorded the incident with his GoPro, and the two give chase to retrieve the footage. In the car, they read a scene sent by Janelle where Slattery's character, sidekick Barnaby, betrays Wonder Man for a price. They spot the boy, Jayden, who tells them that he will erase the footage if Simon helps him get back his stolen motorcycle from a man named Esteban. Arriving at Esteban's house, Esteban tells them that Jayden is lying. The drug dealers arrive and hold Jayden hostage in exchange for Slattery. Esteban's friends help Slattery delete the footage from Jayden's GoPro as the police arrive and engage in aballoonfight with the drug dealers. Jayden reconciles with Esteban while Simon and Slattery flee. They learn from Janelle that the next round of auditions are at Kovak's house and have been moved up to that day.

Simon and Slattery drive to Kovak's mansion for the call back, joining other actors who are in the running to portray Wonder Man and Barnaby. After staying up all night trying to get the GoPro footage, Simon is exhausted. Kovak pairs up the actors and gives them improvisation exercises. While Slattery impresses the group, Simon falters by recreating a scene from the film Pretty Woman rather than using his own experiences and emotions. He later falls asleep and dreams that he uses his powers tohug one of the other actors after that actor calls Simon a freak. Simon confides in Slattery that he is nervous about exposing his powers, but Slattery explains that he is more than his powers and encourages him to show the emotions that he has been keeping inside. Simon and Slattery are paired together and give a performance that impresses Kovak, leading him to cast them both in the film. After Simon drives him home, Slattery is picked up by the DODC and berated by Cleary for taking too long. Slattery confirms that Simon has powers and asks Cleary to give him more time to collect evidence.

Filming for Wonder Man begins. Simon struggles to be personable with the crew and to communicate his thoughts on the script, but is helped by Slattery. Janelle informs the pair that The New York Times journalist Kathy Friedman is writing a profile on them, terrifying Simon who describes Friedman as a character assassin who could discover and reveal his secret. He becomes paranoid after learning that Friedman talked to Vivian, Martha, and Eric about him. Vivian reveals to Simon that she knows he has powers, but she did not say anything about them to Friedman. During Friedman's interview with Simon and Slattery, Simon is surprised to learn that Eric spoke highly of him. Friedman grills Slattery about his latest arrest and asks him what government deal he cut to avoid returning to prison, prompting him to walk off. Confronted by Simon, Slattery confesses the truth of his deal with the DODC to spy on Simon but promises that he will find a way to get out of it. Upset and overwhelmed, Simon goes to a Wonder Man soundstage and unleashes a large explosion that destroys the set.

Simon returns to his apartment assuming that he will be caught. Slattery calls him to apologize and says he has a solution: Slattery revives his Mandarin persona and publicly claims responsibility for the explosion. Cleary knows that Slattery is just taking the blame for Simon, but goes along with it because the DODC needs more prisoners to justify their expensive Yucca Valley, California, prison. Following Slattery's arrest, Kovak insists they continue filming and tells Simon to use Slattery's betrayal for the scene where Wonder Man is betrayed by Barnaby. Wonder Man is finished with Pantoliano taking over the role of Barnaby, and the film is a success. Eric says he is proud of Simon. Janelle tells Simon that he now has his pick of what role to take next, and Simon decides to shadow a DODC guard under the guise of making a new film about him. This gives Simon access to the DODC prison, just as Cleary discovers that Simon's powers use ionic energy and proposes to his boss that Simon could be an asset. Simon uses his powers to break Slattery out of prison and fly away with him.