On his 13th birthday, John Egbert receives the latest computer game, an immersive simulation game called Sburb Beta. Working with his friend Rose Lalonde, they discover that the game allows the players to manipulate their reality.
A startling revelation comes, though - an apocalyptic meteor shower is beginning to destroy the world before their very eyes. However, the game gives them tools to escape their fate. John, Rose, and their friends Dave Strider and Jade Harley work together to flee the apocalypse and enter a new dimension called the Incipisphere. The Incipisphere is a world of "warring royalty in a timeless expanse," where the forces of Prospit and Derse struggle for dominion over the realm of Skaia in the chess-patterned Battlefield at its center. The kids are given primary guides - spirits known as Kernelsprites - to help them understand this new setting and the rules of the game. The four of them must fight against the monsters of the dark kingdom, controlled by the Denizens, and free the Consorts of the four planets circling Skaia. They must master the inventory system called the Sylladex, and understand the alchemy system the game provides.
John, Rose, Dave, and Jade slowly learn of their roles as the Heir of Breath, the Seer of Light, the Knight of Time, and the Witch of Space respectively. They must all undertake personal journeys and come to terms with their relationships with their Guardians. They learn they must pass the Seven Gates, reach Skaia, and stop the Black King and Black Queen from destroying Skaia in an event called the Reckoning. However, it’s said that Skaia would buy the kids time by creating defense portals that would redirect the meteors to another place in paradox space – Earth. Some of these meteors are to "seed" laboratories like the Skyship Base on Earth, and carry Exiles – former members of the two kingdoms – to the year 2422, long after the apocalypse, for them to repopulate the Earth. Others spawn anomalies like the Frog Temple, and others become the meteors that hit the kids’ houses in the first place. However, another revelation happens as John eventually reaches a laboratory in the Incipisphere’s outer meteor belt called the Veil, where he uncovers a mysterious ectobiology machine. John accidentally facilitates the kids’ and their guardians’ own existences. They are sent back to the past on meteors during the Reckoning as well, to set in motion the entire chain of events.
