Build a movie plot around this: What does the secret group call themselves? Dumbledore's Army
The answer to this question is:
Harry Potter and his cousin Dudley Dursley are attacked by two Dementors, but Harry manages to drive the Dementors off with a Patronus charm. Shortly thereafter, the Ministry of Magic detect the act of underage wizardry and attempt to have Harry expelled from Hogwarts immediately, but this is modified to a trial later in the summer. After experiencing horrible nightmares depicting the evil Lord Voldemort's return, Harry is awoken by the arrival of an advance guard of wizards who escort him to the headquarters of the Order of the Phoenix, a secret organization founded by Dumbledore. It is only now that Harry discovers that under the Ministry's influence the newspaper The Daily Prophet has launched a smear campaign against anyone who claims that Voldemort has returned, leaving Harry feeling isolated and betrayed by the Wizarding community. Harry and the other members of the Order fly to 12 Grimmauld Place, the home of Sirius Black, where they meet with Sirius, Remus, Ron, Hermione and others. Later, Ron and Hermione express concern about Harry's situation with the Ministry.Harry and Arthur Weasley head to the court where Harry's trial will take place, briefly spotting Lucius Malfoy speaking with the minister on their way. With the help of Dumbledore and Harry's neighbour, Mrs Figg, Harry is cleared of all charges at the Ministry and is allowed to return to Hogwarts. However, during Harry, Ron and Hermione's fifth year at Hogwarts School, the Minister for Magic Cornelius Fudge appoints a new Defence Against the Dark Arts teacher, Dolores Umbridge, a Senior Ministry official who refuses to teach practical magic to her students, as the Ministry fears Dumbledore will organize his own personal wizard army. One day during class, Harry is punished for claiming that Cedric Diggory was killed by Voldemort, which according to the Ministry's official policy is a lie. In Umbridge's office, Harry is forced to write "I must not tell lies" repeatedly as punishment. However, the sentence is magically imprinted on his hand...