Jesse's Gang, alongside Harper, climb the stairs to find a large, void-like world which Harper calls "The Old Builder's World". When climbing the stairs, Jesse's Gang notice that Harper seems to be hiding something. As the group reaches the top of the stairs, Harper pushes them through a door which leads them to the middle of an apparent game of "Spleef", where people play the game to death.
During this battle, Jesse's friends are trapped by members of the Green Team and Jesse must save either Petra or Ivor; whomever he/she does not save, along with Lukas, is killed. Enraged, Jesse knocks down Nell, who eliminated Lukas and Petra/Ivor, and throws back a block of TNT at a Gladiator, Slab (Character), whose fall halts the Game.
Jesse's Gang are then introduced to the Old Builders: Hadrian, Mevia and Otto who explain that Jesse's friends have been sent to a re-spawn zone to work in the Quartz mines, and that the event is known as the "Games" where participants must stay until they win. Jesse demands the Atlas but Hadrian refuses. However, Jesse strikes a deal that if he/she wins the game, the Gang can leave with the Atlas.
Harper then leads Jesse and Ivor or Petra (whomever he/she saved) to the Competitors' Village. In the Village, Jesse is able to convince a Gladiator, Facemeat, to hand over Lukas and Petra/Ivor with the help of Nell. Jesse's Gang also discovers about "Tim", a legendary hero who won the games and took his friends home.
The next day, the Games feature the"Lava Race", a survival-run minigame where players must go through obstacles. The Green Team's leader. Emily, offers Jesse a chance to team with them, which Jesse can accept or decline. However, either way Em pushes Nell of the vines and (determinately) betrays Jesse. Jesse can either save Nell or win the games.
However, in both outcomes, Hadrian will eventually not go by his word and leave the group to face Em, who walks away. It is revealed that Hadrian had a deal with Em and told her to eliminate Jesse, which she failed. Slab then comes to tell Jesse that Hadrian was calling him/her and they needed to report to the palace. In this situation, Jesse can either do as Slab says or can delay their trip to talk to Sebastian, who offers a talk.
In the palace, Hadrian reveals that he has Axel, Olivia, and the EnderCon Usher, Reuben, hostage and that if Jesse does not lose the games, they will remain imprisoned forever. He offers Jesse a new deal that if Jesse loses the games, all his/her friends could go home, which Jesse can accept or decline. Determined to win, Jesse, back in the Competitor's Village, gives a speech to the crowd, inspiring them to come together against the Old Builders. Em also agrees to be a part of this (determinate).
The following day, Jesse is alone while participating in another minigame, "The Walls". Their section, however, is rigged and does not have equal resources. Ultimately, Em helps him/her and Jesse convinces all the teams as well as Slab (Determinant) to come together against the Old Builders.
In a final standoff against Hadrian and Mevia, Jesse dies, but it is revealed Em has freed his/her friends, who give him/her Tim's armor, weapons and tools. Jesse then is able to take down the duo with his/her friends' assistance as Otto gives him/her the Atlas.
Finally, the group reaches the Portal Hallway where Slab determinately returns Lukas' Journal which Lukas dropped when he died, depending on whether Jesse was nice to him. Ivor says goodbye to Harper (determinate) as Otto promises Jesse he will restore the Games to their former glory. Em also determinately accompanies the group back to the Overworld. Back home, Jesse and the Gang admire the treasures they collected during their adventures. Inspired, Ivor runs back to the Portal Hallway as the credits cut in.
In a post-credit scene, Hadrian and Mevia are seen in a world full of either chicken-sized zombies or zombie-sized chickens (as per the choice made in the beginning of the series).