Hermione and Amelia seized the back of Harry's robes not a moment too soon. just then, they heard a burst of song. It was Hagrid, making his way up to the castle, singing at the top of his voice, and weaving slightly as he walked. A large bottle was swinging from his hands. 

"See?" Hermione whispered. "See what would have happened? We've got to keep out of sight! No, Buckbeak!"

 The hippogriff was making frantic attempts to get to Hagrid again; Harry seized his rope too, straining to hold Buckbeak back. They watched Hagrid meander tipsily up to the castle. He was gone. Buckbeak stopped fighting to get away. His head drooped sadly. 

Barely two minutes later, the castle doors flew open yet again, and Snape came charging out of them, running toward the Willow. 

Harry's fists clenched as they watched Snape skid to a halt next to the tree, looking around. He grabbed the cloak and held it up. 

"Get your filthy hands off it," Harry snarled under his breath. "Shh!"

 Snape seized the branch Lupin had used to freeze the tree, prodded the knot, and vanished from view as he put on the cloak.

 "So that's it," said Hermione quietly. "We're all down there... and now we've just got to wait until we come back up again...." 

She took the end of Buckbeak's rope and tied it securely around the nearest tree, then sat down on the dry ground, arms around her knees. 

"Harry, there's something I don't understand.... Why didn't the dementors get Sirius? I remember them coming, and then I think I passed out... there were so many of them...." 

Harry sat down too. He explained what he'd seen; how, as the nearest dementor had lowered its mouth to Harry's, a large silver something had come galloping across the lake and forced the dementors to retreat. 

Hermione's mouth was slightly open by the time Harry had finished.