In the fifth book, Harry Potter and the Order of the Phoenix, Harry must confront the newly resurfaced Voldemort. In response to Voldemort`s reappearance, Dumbledore re-activates the Order of the Phoenix, a secret society which works from Sirius Black`s dark family home to defeat Voldemort`s minions and protect Voldemort`s targets, including Harry. The Order includes many of the adults Harry trusts, including Remus Lupin, Sirius Black, and members of the Weasley family, but also some surprising members; the loyalties of some characters are not so obvious. Despite Harry`s description of Voldemort`s recent activities, the Ministry of Magic and many others in the magical world refuse to believe that Voldemort has returned.

In an attempt to counter and eventually discredit Dumbledore, who along with Harry is the most prominent voice in the Wizarding World attempting to warn of the Dark Lord`s return, the Ministry appoints Dolores Umbridge as the High Inquisitor of Hogwarts. She transforms the school by a dictatorial regime and refuses to allow the students to learn ways to defend themselves against dark magic.Harry forms a secret study group to teach his classmates the higher-level skills of Defense Against the Dark Arts that he has learned. The novel introduces Harry to Luna Lovegood, an airy young witch with a tendency to believe in oddball conspiracy theories. An important prophecy concerning Harry and Voldemort is revealed,and Harry discovers that he and Voldemort have a painful connection, allowing Harry to view some of Voldemort`s actions telepathically. In the novel`s climax, Harry and his school friends face off against Voldemort`s Death Eaters, who include the rich and arrogant Malfoy family. The timely arrival of members of the Order of the Phoenix saves the children`s lives and allows many of the Death Eaters to be captured and imprisoned.