"He's there!" Harry said, spotting Sirius as they rose up beside the window. He reached out, and as Buckbeak's wings fell, was able to tap sharply on the glass. 

Black looked up. Harry saw his jaw drop. He leapt from his chair, hurried to the window and tried to open it, but it was locked. 

"Stand back!" Hermione called to him, and she took out her wand, still gripping the back of Harry's robes with her left hand. 

"Alohomora!"

 The window sprang open.

 "How -- how --?" said Black weakly, staring at the hippogriff 

"Get on -- there's not much time," said Harry, gripping Buckbeak firmly on either side of his sleek neck to hold him steady. "You've got to get out of here -the dementors are coming -- Macnair's gone to get them." 

"Hurry up old dog we don't have time to teach you new tricks." Sirius let out a bark of laughter.

Black placed a hand on either side of the window frame and heaved his head and shoulders out of it. It was very lucky he was so thin. In seconds, he had managed to fling one leg over Buckbeak's back and pull himself onto the hippogriff behind Amelia. 

"Okay, Buckbeak, up!" said Harry, shaking the rope. "Up to the tower -- come on. 

The hippogriff gave one sweep of its mighty wings and they were soaring upward again, high as the top of the West Tower. Buckbeak landed with a clatter on the battlements, and Harry, Hermione and Amelia slid off him at once. 

"Sirius, you'd better go, quick," Harry panted. "They'll reach Flitwick's office any moment, they'll find out you're gone." 

Buckbeak pawed the ground, tossing his sharp head. 

"What happened to the other boy? Ron?" croaked Sirius.

 "He's going to be okay. He's still out of it, but Madam Pomfrey says she'll be able to make him better. Quick -- go --"

 But Black was still staring down at Harry. 

"How can I ever thank -- "

"GO!" Harry, Hermione, and Amelia shouted together. 

Black wheeled Buckbeak around, facing the open sky. 

"We'll see each other again," he said. "You are -- truly your father's son, Harry...." 

He squeezed Buckbeak's sides with his heels. Harry and Hermione jumped back as the enormous wings rose once more.... The hippogriff took off into the air.... He and his rider became smaller and smaller as Harry gazed after them... then a cloud drifted across the moon.... They were gone. 

"This ended surprisingly well. But we screwed the timeline harder than Marvel."