J. Rowling - Harry Potter and the Prisoner of Azkaban

All they could see now was one of Ron’s legs, which he had hooked around a root in an effort to stop the dog from pulling him farther underground—but a horrible crack cut the air like a gunshot; Ron’s leg had broken, and a moment later, his foot vanished from sight.

“Harry—we’ve got to go for help—” Hermione gasped; she was bleeding too; the Willow had cut her across the shoulder.

“No! That thing’s big enough to eat him; we haven’t got time—”

“Harry—we’re never going to get through without help—”

Another branch whipped down at them, twigs clenched like knuckles.

“If that dog can get in, we can,” Harry panted, darting here and there, trying to find a way through the vicious, swishing branches, but he couldn’t get an inch nearer to the tree roots without being in range of the tree’s blows.

“Oh, help, help,” Hermione whispered frantically, dancing uncertainly on the spot, “Please…”

Crookshanks darted forward. He slithered between the battering branches like a snake and placed his front paws upon a knot on the trunk.

Abruptly, as though the tree had been turned to marble, it stopped moving. Not a leaf twitched or shook.

“Crookshanks!” Hermione whispered uncertainly. She now grasped Harry’s arm painfully hard. “How did he know—?”

“He’s friends with that dog,” said Harry grimly. “I’ve seen them together. Come on—and keep your wand out—”

They covered the distance to the trunk in seconds, but before they had reached the gap in the roots, Crookshanks had slid into it with a flick of his bottlebrush tail. Harry went next; he crawled forward, headfirst, and slid down an earthy slope to the bottom of a very low tunnel. Crookshanks was a little way along, his eyes flashing in the light from Harry’s wand. Seconds later, Hermione slithered down beside him.

“Where’s Ron?” she whispered in a terrified voice.

“This way,” said Harry, setting off, bent backed, after Crookshanks.

“Where does this tunnel come out?” Hermione asked breathlessly from behind him.

“I don’t know… It’s marked on the Marauder’s Map but Fred and George said no one’s ever gotten into it… It goes off the edge of the map, but it looked like it was heading for Hogsmeade…”

They moved as fast as they could, bent almost double; ahead of them, Crookshanks’s tail bobbed in and out of view. On and on went the passage; it felt at least as long as the one to Honeydukes… All Harry could think of was Ron and what the enormous dog might be doing to him… He was drawing breath in sharp, painful gasps, running at a crouch…

And then the tunnel began to rise; moments later it twisted, and Crookshanks had gone. Instead, Harry could see a patch of dim light through a small opening.

He and Hermione paused, gasping for breath, edging forward. Both raised their wands to see what lay beyond.

It was a room, a very disordered, dusty room. Paper was peeling from the walls; there were stains all over the floor; every piece of furniture was broken as though somebody had smashed it. The windows were all boarded up.

Harry glanced at Hermione, who looked very frightened but nodded.

Harry pulled himself out of the hole, staring around. The room was deserted, but a door to their right stood open, leading to a shadowy hallway. Hermione suddenly grabbed Harry’s arm again. Her wide eyes were traveling around the boarded windows.

“Harry,” she whispered, “I think we’re in the Shrieking Shack.”

Harry looked around. His eyes fell on a wooden chair near them. Large chunks had been torn out of it; one of the legs had been ripped off entirely.

“Ghosts didn’t do that,” he said slowly.

At that moment, there was a creak overhead. Something had moved upstairs. Both of them looked up at the ceiling. Hermione’s grip on Harry’s arm was so tight he was losing feeling in his fingers. He raised his eyebrows at her; she nodded again and let go.

Quietly as they could, they crept out into the hall and up the crumbling staircase. Everything was covered in a thick layer of dust except the floor, where a wide shiny stripe had been made by something being dragged upstairs.

They reached the dark landing.

“Nox,” they whispered together, and the lights at the end of their wands went out. Only one door was open. As they crept toward it, they heard movement from behind it; a low moan, and then a deep, loud purring. They exchanged a last look, a last nod.

Wand held tightly before him, Harry kicked the door wide open.

On a magnificent four poster bed with dusty hangings lay Crookshanks, purring loudly at the sight of them. On the floor beside him, clutching his leg, which stuck out at a strange angle, was Ron.

Harry and Hermione dashed across to him.

“Ron—are you okay?”

“Where’s the dog?”

“Not a dog,” Ron moaned. His teeth were gritted with pain. “Harry, it’s a trap—”

“What—”

“He’s the dog… he’s an Animagus.”

Ron was staring over Harry’s shoulder. Harry wheeled around. With a snap, the man in the shadows closed the door behind them.

A mass of filthy, matted hair hung to his elbows. If eyes hadn’t been shining out of the deep, dark sockets, he might have been a corpse. The waxy skin was stretched so tightly over the bones of his face, it looked like a skull. His yellow teeth were bared in a grin. It was Sirius Black.

“Expelliarmus!” he croaked, pointing Ron’s wand at them.

Harry’s and Hermione’s wands shot out of their hands, high in the air, and Black caught them. Then he took a step closer. His eyes were fixed on Harry.

“I thought you’d come and help your friend,” he said hoarsely.

His voice sounded as though he had long since lost the habit of using it.

“Your father would have done the same for me. Brave of you not to run for a teacher. I’m grateful… it will make everything much easier…”

The taunt about his father rang in Harry’s ears as though Black had bellowed it. A boiling hate erupted in Harry’s chest, leaving no place for fear. For the first time in his life, he wanted his wand back in his hand, not to defend himself, but to attack… to kill. Without knowing what he was doing, he started forward, but there was a sudden movement on either side of him and two pairs of hands grabbed him and held him back…

“No, Harry!” Hermione gasped in a petrified whisper; Ron, however, spoke to Black.

“If you want to kill Harry, you’ll have to kill us too!” he said fiercely, though the effort of standing upright was draining him of still more color, and he swayed slightly as he spoke.

Something flickered in Black’s shadowed eyes.

“Lie down,” he said quietly to Ron. “You will damage that leg even more.”

“Did you hear me?” Ron said weakly, though he was clinging painfully to Harry to stay upright. “You’ll have to kill all three of us!”

“There’ll be only one murder here tonight,” said Brack, and his grin widened.

“Why’s that?” Harry spat, trying to wrench himself free of Ron, and Hermione. “Didn’t care last time, did you? Didn’t mind slaughtering all those Muggles to get at Pettigrew… What’s the matter, gone soft in Azkaban?”

“Harry!” Hermione whimpered. “Be quiet!”

“HE KILLED MY MUM AND DAD!” Harry roared, and with a huge effort he broke free of Hermione’s and Ron’s restraint and lunged forward—

He had forgotten about magic—he had forgotten that he was short and skinny and thirteen, whereas Black was a tall, full grown man—all Harry knew was that he wanted to hurt Black as badly as he could and that he didn’t care how much he got hurt in return—