In the beginning of the film, Loki is once again banished from Asgard and finds himself stranded in Springfield. There, he crosses paths with Bart Simpson, who is in the middle of causing chaos in town with his shenanigans. The two form an unlikely alliance when Loki offers to help Bart pull off a grand prank on the whole town, in exchange for his help in creating a portal to return to Asgard.
As they work together, they encounter several superheroes and villains from the Marvel universe who have also somehow gotten trapped in Springfield. This includes Iron Man, Black Widow, Hulk, Spider-Man, and more. They team up to defeat Loki's old nemesis, Thanos, who has also found himself trapped in Springfield and is causing mayhem.
The climax of the film involves a massive battle between the heroes and villains, with Bart and Loki proving to be a formidable duo. In the end, they successfully create a portal to return to Asgard, bidding farewell to their newfound friends from the Marvel universe. The Simpsons and their Springfield neighbors are left to pick up the pieces of the battle and rebuild their town once again.