At daybreak the morning after Mr. Crouch attacked Krum, Harry, Ron, and Hermione are at the Owlery, sending an update to Sirius and discussing possible and unlikely explanations for the strange events of the evening. Fred and George enter the Owlery discussing blackmail and preparing to send a letter, and the five students regard each other warily; ultimately none of them reveal their purpose. Later that morning, Harry, Ron, and Hermione visit Professor Moody, who reports that Mr. Crouch did not show up on the Marauder's Map-very odd indeed, as he did not seem in the sort of state where he could have escaped the premises quickly. Moody warns Harry to be especially careful; soon after, Harry receives a letter back from Sirius, also warning him to be especially careful, as somebody who is obviously very dangerous is at Hogwarts and may be after Harry. Sirius warns him further to prepare well for the third task, which he does, with the help of his friends.
Several days later, in Divination class, Harry falls asleep to the heat and to the droning of an insect, and he dreams of flying on an owl into a house, inside of which Voldemort is reprimanding Wormtail for having made some mistake, noting that some unnamed "he" is dead, and foretelling that soon he would have Harry Potter dead and ready to be fed to his pet snake. Voldemort then applies the Cruciatus curse to Wormtail, causing Harry to wake up screaming and clutching his scar. Harry leaves the room and charges towards Dumbledore's office, where he can hear Cornelius Fudge and Moody arguing with Dumbledore. Moody sees Harry through the door and announces his arrival.
Harry waits in Dumbledore's room while the three adults examine the grounds for clues; as he waits, he observes Fawkes, Dumbledore's pet phoenix, and he also notices in a half-open cupboard a basin containing something silvery and swirling. Harry studies it, pokes it with his wand and looks closer, ultimately touching his nose to it and falling in; he lands in a courtroom, where he is an unseen observer among a grave audience (including a slightly younger Dumbledore and Moody). Harry watches as Karkaroff is strapped into a chair at the room's center and questioned by Mr. Crouch, who has agreed to set him free from Azkaban in exchange for the names of other Death-Eaters. Karkaroff gives many names, including Snape-but Dumbledore stands up and vouches for Snape, who had left Voldemort and agreed to work as a spy for the good side. Suddenly the room dissolves, and Ludo Bagman is sitting in the same chair, pleading that he didn't realize that he was working for Voldemort's supporters. The audience votes to forgive him, presumably due to their admiration of his Quidditch abilities. The room dissolves a third time and reveals Mr. Crouch's son in the center of the room, pleading to be let go, while his strict father accuses him of many awful things, including subjecting the Longbottoms to the Cruciatus curse. Mr. Crouch's wife is weeping in the audience as Mr. Crouch sentences his only son to a lifetime in Azkaban.
Dumbledore pulls Harry out of the room and back into his office, where he explains that the basin is a Pensieve, a holder for excess thoughts and memories. He does not seem at all upset that Harry was poking around in his office. Harry tells Dumbledore about his dream, and Dumbledore expresses his belief that the dream is probably true, that Voldemort is near and dangerous, and that the three recent disappearances of Bertha Jorkins, Mr. Crouch, and a Muggle named Frank Bryce, may be traceable to Voldemort. Harry considers this, then asks whether the Longbottoms mentioned were Neville's parents. Dumbledore replies bitterly that they are, and says that they were very popular Aurors who went insane after being subjected to the curse, which is why Neville lives with his grandmother. Harry asks also whether Bagman or Snape has been convicted of any Dark activity since that time. Dumbledore answers, with conviction, that neither has, before bidding Harry goodbye and good luck on the third task.
Rowling uses similar devices in the books in the series to explain events that occurred before harry's lifetime. In this novel, as well as in Harry Potter and the Chamber of Secrets, Harry is granted entrance into hidden mysteries of the past through a magical memory-saving device. In The Chamber of Secrets, it was Tom Riddle's diary; in this case, it is Dumbledore's Pensieve (thought-preserver). These devices give both Harry and us a clear understanding of the past without learning it directly from another character in the book. In each case, he witnesses the past first-hand, and he uses the information he gains to help solve the mystery at the end of each book. Here, Harry sees things from Dumbledore's memory, a method for him to learn from the headmaster without compromising Dumbledore's integrity. Even after looking into the Pensieve, Harry is spared a great deal of information, such as the true story of Dumbledore's forgiveness of Snape. This still lingers as a mystery, and will probably not be resolved until a later book. But we see Dumbledore's faith in Harry when he explains the story of Neville's parents and trusts Harry not to tell anyone.
The vision allows Harry to understand events that he is not present to witness. The dream that awakens him in Chapter One is true, suggesting that this dream might also offer some portent of Voldemort's whereabouts and plans. Harry reports his dreams to figures of authority, and he uses his visions in the Pensieve to gain a fuller understanding of certain characters who seem already to have shady pasts, but whose exact roles Harry does not yet know. Harry already has been placed in situations of responsibility unusual for a boy his age. This method of informing him via a dream is especially important, because it places him alone in a situation where he can have no external help. As most of his battles require some assistance, his dream-encounters with Voldemort represent the ultimate loneliness and helplessness. He has no option but to face Voldemort alone. To make Harry's efforts legitimate, he must do this battle alone; by taking him away from Hogwarts castle, or by unconsciously entering into his dreams, Voldemort can corner Harry.