Prof. Abditus Questor

Book 5: Harry Potter and the Order of the Phoenix
PLOT SUMMARY: Harry, feeling neglected and resentful at Privet Drive with no news of Voldemort or the Order of the Phoenix, is attacked by a pair of Dementors, which he drives off with his Patronus. Then he is taken to the headquarters of the Order of the Phoenix at No. 12, Grimmauld Place. On his return to Hogwarts, he finds that Dolores Umbridge is Dark Arts instructor but teaches only theory, without practice. She eventually takes over the running of Hogwarts. So Harry begins secretly to instruct a group of students called "Dumbledore's Army" in practical self-defense. Harry has a vision that he is inside a snake biting Arthur Weasley, who ends in St Mungo's Hospital for Magical Maladies and Injuries, where Harry and the Weasleys visit over Christmas. Prof. Snape is supposed to teach Harry Occulmency, to prevent Voldemort from invading his mind. But the lessons go badly until Harry accidentally gets access to Snape's memories of his father' boorish behavior as a young man; Snape refuses to continue the lessons. Hermione gets an interview with Harry published, which alerts people to the facts of Voldemort's return. Hagrid returns from a trip unsuccessfully to enlist the giants on Dumbledore's side, but he brings back with him his half-brother, the giant Grawp. Harry has another vision that Voldemort is torturing Sirius in the Department of Mysteries, but it is an illusion planted by Voldemort to trick Harry into coming there, so he can be forced to retrieve a prophecy concerning himself and Voldemort that the latter wants to know. Harry goes and is trapped by the Death Eaters. A band of the Order of the Phoenix, including Sirius, come to rescue him, but Sirius is killed by his cousin, Bellatrix Lestrange. After Dumbledore gets Harry back to Hogwarts, he explains that the prophecy means that either Harry or Voldemort must kill the other. But that is not predetermination; rather it is a consequence of Voldemort's having identified Harry as the one of whom the ambiguous prophecy spoke, thus forcing Harry to respond or be killed himself.
QUEST: Harry's general quest in this book is to go through his Dark Night of the Soul and particularly to learn what secret weapon Voldemort wants (the prophecy) and why Voldemort has been trying to kill him.