Three years after the events of Jumanji: Welcome to The Jungle, Spencer, Fridge, Bethany, and Martha have gone their separate ways though the four of them plan to see each other again on Christmas break. Spencer, however, turns out to be a no-show and the three of them soon realize it's because Spencer missed playing as his avatar Dr. Smolder Bravestone, so he went back into the world of Jumanji.
Anthony "Fridge" Johnson and Martha get pulled into the game as well by a bright green mist before they can decide who they want to play as. After entering the world of Jumanji, Dr. Sheldon "Shelly" Oberon is anything but happy about Bethany not playing as him. The group then meets up with Nigel Billingsley and Dr. Smolder Bravestone, thinking it will be as easy as it was last time is proven wrong when Nigel Billingsley explains that the rules of the game have changed since the last time they played and that they must retrieve a magic amulet that Jurgen the Brutal stole to win the game. The group just barely manages to outrun an angry pack of ostriches before setting out on their long journey to find the amulet which eventually at one point takes them to a marketplace where Spencer is revealed to be playing as Ming Fleetfoot, a new avatar.
The group finally catches up with Alex and Bethany, revealed to be playing as Jefferson "Seaplane" McDonough and Cyclone the horse respectively who lead the group to a river with the same glowing green water that swapped everyone's personalities and avatars. The group changes into winter gear for their trek into the castle where Jurgen the Brutal is guarding the amulet. Franklin "Moose" Finbar and Dr. Sheldon "Shelly" Bravestone tell the two guards guarding the castle entrance that they are the Brothers Kababab and the guards buy it and grant the two entrance. Their cover is soon blown however when Jurgen the Brutal realizes their true intentions and orders his men to seize the two (and Ruby Roundhouse who fights all of Jurgen's men by herself).
Jurgen then makes his getaway on his airship but not before Dr. Smolder Bravestone follows him aboard, determined to win the game. After a back and forth fight between Dr. Smolder Bravestone and Jurgen the Brutal, Jurgen falls to his death from the airship. With the amulet safely returned to Nigel Billingsley, Milo as Cyclone decides to stay in the world of Jumanji while Eddie as Ming Fleetfoot admits he's going to miss him and wishes him luck with his decision. After returning to the real world, Spencer and his grandfather are seen playing video games.
The repairman finally stops by in a mid-credits scene and sees the game controller for the Jumanji game and picks it up, unknowingly releasing the ostriches, mandrills, and other wild animals from the game into the real world just as Bethany, Martha, Anthony "Fridge" Johnson, and Spencer take a minute to process what they just saw with a look of surprise on their faces.
