2045. Earth is on the verge of collapse due to corruption, overpopulation and pollution, and people prefer to live in the OASIS, a virtual reality world created by James Donovan Halliday (Mark Rylance).
Halliday dies, leaving a message in which he reveals that whoever completes three quests and finds a hidden Easter Egg will inherit his fortune and complete control of the OASIS. The IOI Corporation run by Nolan Sorrento (Ben Mendehlson) becomes determined to find the Easter Egg and employs indentured users known as “Sixers” to search for it.
Teenager Wade Watts (Tye Sheridan) lives in the slums of Columbus, Ohio, with his aunt Alice (Susan Lynch) and her boyfriend Rick (Ralph Inneson) and dreams of finding the Easter Egg to change their lives.
Wade’s avatar, Parzival, and his best friend, the orc Aech, join the first quest, an obstacle race through a shifting cityscape, which nobody has managed to complete. They lose, but Parzival saves famous player Artemis from being “zeroed out” in the process.
Parzival later visits the Halliday Archives in search of clues and learns about Halliday’s falling-out with his business partner and best friend, Ogden Morrow (Simon Pegg), which Halliday wishes he could “reverse”.
In the next race, Parzival shifts into reverse and finds a safe path to victory, which is followed by Artemis, Aech and twins Daito and Shoto. They appear on the global scoreboard and become known as “The High Five”.
Sorrento learns Parzival’s identity and attempts to recruit Wade to work for IOI. When he refuses, Sorrento’s enforcer Zandor (Hannah John-Kamen) blows up the slums, killing Alice and Rick, while Artemis’ user, Samantha Cook (Olivia Cooke), rescues Wade.
Samantha finds out that Halliday loved a woman, Kira, who ultimately married Morrow, leading to their falling-out. Parzival and his friends return to the Halliday Archives and find the entrance to the second quest in Halliday's hidden memories of Kira.
