Harry Potter, Hermione Granger and Ron Weasley enter their fourth year at Hogwarts school. The film opens in a graveyard attached to an old country house; the gardener Frank Bryce awakes in his cottage to see a light on in the (deserted) house. He investigates to find Lord Voldemort and Peter Pettigrew, discussing plans with an unidentified man; Bryce is eventually killed by Voldemort. Harry awakes at The Burrow before departing with the Weasley family and Hermione for the 422nd Quidditch World Cup. After the introduction to the game, there is a temporal jump to that evening, when the camp is attacked by Death Eaters, who disperse when the Dark Mark is shot into the air by an unkown man.

For the third task, the Triwizard cup is placed inside a large maze, whose magical hedges are capable of attacking the champions as they attempt to reach it: the first champion to touch the cup will be declared the winner. Having saved each other several times throughout the tournament, Harry and Cedric reach the cup together and decide to claim a draw, both touching the cup at the same time. The cup, which is actually a portkey, transports the two to a graveyard, where Wormtail appears with a form of Voldemort. Upon command, Wormtail kills Cedric and traps Harry against an enchanted tombstone. Wormtail performs complicated magic involving taking blood from Harry's arm, which eventually returns Voldemort to a corporeal body. After explaining how he lost his powers to Harry, Voldemort duels Harry. Thanks to a rare magical effect, Harry is able to escape by summoning the cup, which takes him back to Hogwarts. Moody takes Harry to his office; he suddenly starts to change his appearance when he learns that he has ran out of Polyjuice Potion. Moody reveals that he is in fact an escaped Death Eater who has been impersonating Alastor Moody all year, in order to help Harry win the Triwizard tournament and hence reach the cup first. Harry was not supposed to survive or return; as Moody is about to kill Harry, Dumbledore, Snape, and McGonagall burst in the room and stun him. The imposter rapidly changes from appearing like Moody to his own appearance, Barty Crouch Jr. The film closes as the foreign schools depart after Dumbledore exhorts them to stand together against Voldemort.