|| Barty Crouch Junior is revealed to be the Death Eater living at Hogwarts, using Polyjuice Potion to disguise himself as Alastor Moody during Harry's fourth year. He kept the real Mad-Eye Moody in a trunk in his office to be able to steal his hairs to make the Potion, and to question the retired Auror about his habits and his past, allowing him to fool even Dumbledore.
Crouch Junior removes Harry from the Quidditch pitch after the third task and escorts the boy up to Moody's office, asking him questions about the events that night. He reveals to Harry that he was the one who conjured the Dark Mark at the Quidditch World Cup campsite, and who put Harry's name into the Goblet of Fire. Under the guise of Alastor Moody, he frightened off those who thought to prevent Harry from winning the Triwizard Tournament, and encouraged Hagrid to tell Harry about the dragons. He gave Cedric the clue to deciphering the golden egg, knowing that the boy would want to repay Harry's help with the first task. He staged a loud conversation with Professor McGonagall to let Dobby know about the second task, knowing that the house-elf would do anything to help Harry. During his patrol of the maze, he Stunned Fleur Delacour and put the Imperius Curse on Viktor Krum, compelling the boy to attack Cedric Diggory. Crouch Junior is determined to kill Harry in Moody's office, but is Stunned by Professor Dumbledore before he can do so.
Barty Crouch Junior is given three drops of a Truth Potion and revived by Professor Dumbledore after the effects of the Polyjuice Potion have worn off. He is questioned by Dumbledore about his escape from Azkaban, and reveals that it was his father who smuggled him out of the prison, swapping places with his dying mother. Crouch Junior was kept under the influence of the Imperius Curse by his father after the escape, and was cared for by Winky the house-elf. He was taken by his father and Winky to the Quidditch World Cup, his father having been persuaded by the house-elf. Crouch Junior was starting to fight his father's Imperius Curse at the time, and there were brief periods when he seemed outside of Mr Crouch's control. He was hidden by an Invisibility Cloak and seated in the Top Box, protected by Winky. He stole Harry's wand during the match, the first he had held since before his imprisonment in Azkaban. He was angered during the chaos at the World Cup campsite when he heard the Death Eaters outside his tent, hating them for turning their backs on Lord Voldemort, and wanted to attack them. He was forced away from the campsite by Winky, who used her own brand of magic to bind them together. After conjuring the Dark Mark, both Barty Crouch Junior and Winky were hit by Stunning Spells, Crouch Junior remaining hidden by the Invisibility Cloak he was wearing. He was discovered by his father and returned home.
Barty was freed from his father's control by Lord Voldemort. He agreed to be placed at Hogwarts as Voldemort's loyal follower, his greatest ambition being the opportunity to prove himself to the Dark Lord. Together, he and Wormtail prepared the Polyjuice Potion and kidnapped Alastor Moody, and he took the Auror's place immediately, managing to persuade Arthur Weasley that the commotion caused by their attack was merely a case of enchanted dustbins. He travelled to Hogwarts disguised as the ex-Auror, taking the real Moody with him in his trunk. Barty killed his father after he escaped to Hogwarts, using the Marauder's Map to time his arrival at the scene, and the subsequent disposal of the body. On the night of the third task, he offered to take the Triwizard Cup into the maze before dinner. He transformed the Cup into a Portkey, ready for the next part of his master's plan.
An insane smile lights Barty Crouch Junior's features as he tells his story to those in Moody's office. His head droops onto his shoulder, unconscious, as he finishes speaking.