Order of the Phoenix --- 31-34

Chapter 31: O.W.L.S.
The tests are finally upon them and everyone is studying furiously in order to do their best. As they get underway, tensions are high but Harry is fairly pleased with his performance.
The night of his Astronomy practical is warm and clear, and as Harry fills out his star chart he's astounded when, from the top of the Astronomy Tower, he watches Hagrid get attacked by Umbridge and 5 other shadowy figures out on the grounds. With mounting horror he watches as McGonagall rushes to Hagrid's defense and gets Stunned by 4 of the figures. Hagrid manages to escape and disappears into the Forbidden Forest.
His last exam takes place the next morning, and as Harry tries to concentrate he falls asleep and has a terrifying dream. Voldemort has captured Sirius and is torturing him in the Department of Mysteries. Harry screams, and wakes up suddenly back in the Great Hall.

Chapter 32: Out Of The Fire
Harry is frantic. He quickly tells Ron and Hermione about his vision, and Hermione tries to interject some sense into Harry, saying there is no way Voldemort could have gotten to Sirius. She urges him to use Umbridge's fire to check on Sirius at Grimmauld Place before he goes off to do something rash and dangerous.
Harry is almost insane with worry about Sirius but he agrees. They station Ginny and Luna as lookouts and have Umbridge drawn away from her office with a diversion. When Harry and Hermione stick their heads in the fire to check on Sirius they only see Kreacher, who leads them to believe that Voldemort has indeed taken him captive.
Umbridge, who saw right through their diversion and had the Inquisitorial Squad capture Ron, Ginny, Luna, and Neville as well, pulls them suddenly from the fire. She sends for Professor Snape, intending to force Harry to drink Veritaserum so she can find out who he was talking to. Harry hurriedly tries to send Snape a cryptic message about Sirius, but is not sure he understands.
Just as Umbridge is about to do the unthinkable and torture Harry for information, Hermione comes up with an elaborate lie, and lures Umbridge into the Forbidden Forest with her and Harry.

Chapter 33: Fight And Flight
Harry has no idea what Hermione's plan is, but he follows her into the forest, hoping she knows what she's doing. They're quickly surrounded by an angry group of centaurs, who grow even angrier when Umbridge insults them. They carry her off and are about to kill Harry and Hermione when Grawp comes to their rescue, causing enough of a diversion to allow them an escape.
Just as Harry's temper is about to explode with impatience they meet up with Ron, Ginny, Neville, and Luna, who managed to escape the Inquisitorial Squad. Luna comes up with the brilliant idea to fly to the Ministry of Magic using the thestrals, and Harry quickly agrees to the plan.

Chapter 34: The Department Of Mysteries
Once they make it to the Ministry Harry leads them to the door he's been dreaming about for months. They search slowly through one room after another, looking for the one where Sirius is being held. They encounter a number of very strange objects and finally find the correct room. They race through, looking for Sirius, and Harry is sickened when he realizes he's not there. Ron finds a dusty orb with Harry's name on it, and as soon as Harry takes it off the shelf they are surrounded by Death Eaters.

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