Stuart Ashen is introduced as a sneak-thief who steals rare but worthless items, primarily electronics, for historical preservation. His partner, Benny, works with him but is frustrated at not receiving equal credit for their successes. Benny informs Stuart that he has been researching "Polybius", the famous lost arcade machine that drove players mad, and has obtained an archive photo of the lead developer - whom Stuart recognizes as Jonathan Ashen, his father. Stuart recalls Jonathan abandoning him and his sister to work full-time on a "secret project", telling them that Stuart's grandfather, Woodward, spent his life trying to create a portable organ which did not work, and two coin-shaped tokens which were supposed to grant free play on any arcade machine but in fact shorted out any machine they were put into. Benny has also learned that the Polybius machine may be in the hands of Anthony Agonist, a millionaire businessman with an obsession with the new and modern, and in storage at his facility in the city's Bowthorpe Park Industrial Estate.Stuart visits a professor at the Institute of Outdated Technology who confirms that Polybius is dangerous, especially in the hands of Agonist, and that the developer was obsessed with completing it, even after it become clear it was causing serious harm, until the military blocked the project. Stuart and Benny assemble a team to break into Agonist's facility, consisting of Annalise, a tech fixer; Vocal, a voice actress and impersonator; Jarred, a "smooth talker" who can infiltrate the staff; Cube, a tech expert who dislikes Stuart's interest in older tech; Jeff, the financial sponsor; Yiannis, a Greek accidentally recruited by Jeff after misunderstanding Stuart's request for a "grease man"; and Ryan, the only one with a driving license. Stuart then recruits two more strangers so that there can be 11 team members and sends them out to raise additional funds on the streets.Stuart visits his sister, Christine, who has become obsessed with lawnmowers as a result of their father's last words of advice and is detached from Stuart. She denies knowing anything about Polybius and refuses to co-operate, but it is shown that in fact she is employed by Anthony Agonist to reverse-engineer the game. Agonist is obsessed with the new as a result of having grown up using only old items that were hand-me-downs from his four older brothers, and intends to use the Polybius to create "Polybius 2.0", an impossibly addictive mobile app that will also brainwash players with his obsession.Jarred gets a security job at Agonist's facility and installs a hidden camera behind the security desk, but is unable to establish the name of the chief scientist who would have access to the machine. Stuart and the rest of the crew invite Agonist over to Stuart's office with the claim that they are intending to demolish a museum, but actually to obtain Agonist's fingerprint on a water glass; however, Agonist turns up early before Benny can leave with the fingerprint scanner, and refuses the drink of water, but then picks up the scanner and scans his own prints anyway because he likes to play with cool new gadgets. He also mentions to Stuart that his sister is the chief scientist on the project. Christine, meanwhile, becomes suspicious and makes an internal request for the Polybius machine to be moved to a new location, which is intercepted by Cube who informs the crew that they must now complete the heist within two days.Arriving at the facility, Cube and Stuart install a hijacking device in the underground data center and disable the CCTV, explaining that they will only have 30 minutes before it is re-activated. Stuart and Benny approach the desk claiming to be scientists, using the hidden camera's view of the guest list to give the name of an expected visitor, and bypass the inner security measures by using a cast of Agonist's finger and a printed-out photograph of Agonist to bypass a facial scanner (to the fury of Cube who had previously hacked the facial database). Meanwhile, Jarred tries to charm and distract Christine in order to steal the unlocking device for the storage room, but fails to do so until he identifies her obsession with lawnmowers and seduces her by describing the process of starting a ride-on mower.Stuart reaches a door with instructions written in Greek, requiring Yannis to be fetched at short notice to translate. He then bypasses a laser motion detector by moving extremely slowly, disabling it when he reaches the other side, and Cube captures the output from the stolen unlocking device to forward to a device held by Stuart to unlock the storage room. Stuart and Benny are unable to steal the entire upright Polybius cabinet, but Stuart removes the ROM, explaining that all other parts of the machine are standard.Anthony Agonist has intercepted Christine's request to move the Polybius machine and arranges to meet her in the storage room. Expecting to meet Christine, he instead finds Stuart and Benny trying to steal the ROM, but is interrupted when Benny snatches the ROM from Stuart and flees, re-activating the motion detector as he goes. Agonist attempts to chase Stuart while both are moving extremely slowly through the laser movement detectors, but attempts to rush forward when Stuart escapes the grid, activating the security system which subdues him. Stuart and the entire crew are forced to flee the facility as alarms sound all around, but Stuart abandons the crew in fury that he has been betrayed.Christine visits Stuart in his office where she explains that she suspected Stuart was aiming to steal Polybius for reasons to do with their father rather than simply to frustrate Agonist, and he agrees. She explains that she planted a GPS tracker on the ROM in anticipation of it being stolen and Stuart realizes that this can be used to track down Benny. He apologizes to the crew for storming out and they head out to find the ROM.Stuart tracks Benny down, and Benny reveals that due to his frustration at not being given credit for his work, he deliberately manipulated Stuart into stealing the ROM in order that he could betray him and hand it over to his new employer - Jonathan Ashen. Jonathan explains that he left to pursue the project exclusively in order to avoid the same humiliation that Woodward suffered, of giving his life to a work and failing. He has asked Benny to recover the Polybius ROM in order that he could obtain it without being detected by the military, and work independently to complete the project regardless of the danger involved. Jonathan asks Stuart to work with them, but he refuses and is knocked unconscious by Benny.Stuart awakens on a rooftop where Benny and Jonathan have installed the Polybius ROM into an arcade cabinet connected to a power transmitter which will "test" Polybius on the screen of every active gaming device for miles around. Christine, who has been in pursuit of Stuart, also arrives and tries to convince Jonathan to stop, but he refuses and starts the machine, throwing gamers in the area into fits. However, Ashens' crew are in hiding and Cube uses his hacking device to jam the transmitter. While Jonathan leaves to try and re-activate the transmitter, Stuart and Christine rush forward and place their grandfather's free-play coins into the cabinet, shorting it out. The crew flees and Stuart attempts to bring his father with them, but he insists on attempting to fix the cabinet and is apparently killed when the cabinet explodes, destroying the ROM.Ashens' crew return to their hideout and celebrate; Cube releases Agonist's dubious financial records publically, resulting in the collapse of his company. The crew also find that of the two strangers recruited to make up the numbers, one has mysteriously died but the other has raised over 100,000 pounds by street fundraising, so they decide to go on a group holiday to Grimsby. Post-credits scenes reveal that Benny is now working at a comic shop being harassed by fans, Agonist is unsuccessfully trying to sell his 4th autobiography at yard sales, and Stuart used some of the money to buy Christine a ticket on a lawnmower-themed cruise event, to which she invites Jarred.