"I have to go home," said Remus one evening in mid-October. "My mum's illness is flaring up again."

Peter pretended to look surprised, though really he'd been waiting for this ever since Remus had started looking sickly again last week. "Oh, no!" he exclaimed, sitting forward on his bed. "That's terrible."

"Aw, Re, you're gonna miss the lunar eclipse tonight," James added. "Sinistra's been prattling on about it for months."

"I know," Remus said regretfully, buttoning up his coat. "I wish I could stay for it." He finished with the coat and tied up his duffel bag, ruffling his hair with a sigh. "You'll tell me about it when I get back, right?"

"'Course, Re," Sirius promised. "Though I'm sure you can see the eclipse in Wales, too."

Remus smiled. "Right; of course. I'll see you guys later." He grabbed his bag and gave them all a quick wave goodbye before vanishing down the stairs.

The boys waited for about five seconds before scrambling for their shoes. "Get the cloak," Sirius hissed to James, who pulled it out from under his bed and threw it over the two of them. "Peter!" Peter gave up halfway through tying his shoe and ran over to his friends, slipping underneath the cloak between them.

"All right," James breathed as he led them forward towards the door. "Remember: fast and quiet. Like Peeves running from the Bloody Baron." Peter laughed; Sirius slapped a hand over his mouth to shut him up.

The three of them made it down into the common room and out into the hallway; Remus was at the far end of it, turning to head down a flight of stairs. James put an arm around Peter and pulled him forward after their roommate, Sirius keeping pace on Peter's other side.

They followed Remus down through the maze of staircases and up to the entrance of the hospital wing, lurking a good distance back so they wouldn't be overheard. "Why's he going to the hospital wing already?" Sirius wondered. "I thought he had to get himself beat up first." Peter shook his head, feeling more confused than ever.

"Well, one thing's for sure," James said. "He's not going home to his sick mum."

Madam Pomfrey opened the door to the wing and brought Remus's bag inside. She then emerged again and led him in the direction of the castle entrance hall. His three roommates exchanged glances under the cloak and followed, through the hall and out the front doors onto the castle grounds.

"Where are they?" Sirius hissed once they were outside. Peter was the one who spotted them first: they were climbing the hill leading up to the feared Whomping Willow tree, a tree Peter had never dared to get within thirty feet of. He pointed to Remus and Pomfrey wordlessly.

"The Willow?" James asked. "What the hell are they doing?"

"Come on!" Sirius took off down the stone steps leading from the castle door, forcing James and Peter to follow. But Peter was distracted watching Remus and Pomfrey climb closer and closer to the tree, so close now that they could be whacked down by its branches….

Sirius stepped on his untied shoelace, and Peter tumbled down the steps, dragging the other two with him and sending the Invisibility Cloak flying. "Ow!" James yelped, hitting his head hard on the stone. "Bloody hell, you guys!"

Sirius recovered first, pulling himself off the steps and racing to grab the cloak and cover them up before they were noticed. "Peter, tie your shoes next time," he hissed in Peter's ear.

"Sorry," Peter squeaked. "I—I didn't have time."

"Oh, damn it," sighed James. "Where did they go?"

Remus and Pomfrey were gone, vanished as if they'd been swallowed up by the earth. "Did they Disapparate?" Peter wondered.

James rolled his eyes. "You can't Disapparate on school grounds," he said. "It's impossible."

"Well, where did they go, then?" Where could they have gone? There were no doors anywhere to vanish through, no tunnels to hide away in.

"Wherever it is, I'm sure it has something to do with the Whomping Willow," James said firmly. "That's what they were headed, wasn't it?"

"Oh, no," Peter whimpered. "I don't want to go near it. Davey Gudgeon nearly lost an eye when he got too close."

"We're not going to let you lose an eye, Peter," sighed Sirius. "But you have to come with us, mate; we've only got one Invisibility Cloak."

So Peter reluctantly followed them up the hill to the Willow. Its branches began to quiver as they approached, warning them not to get any closer. It seemed to know they were there despite the cloak hiding them from view. Peter supposed the tree didn't have eyes, anyway; it was using something else to sense them.

And then, suddenly, the ground beside its trunk ripped open, and out climbed Madam Pomfrey, shaking cobwebs off of her gown. The Willow's limbs froze until she was safely out of their reach; then the ground sewed itself back up and the tree reverted to its moving, angry self. With one quick glance behind her, Pomfrey headed back down the hill and towards the castle, passing only a few feet away from the boys under the cloak.

"What the hell was that?" Sirius breathed once she was gone. "Did she just trap Remus under the Whomping Willow?"

James shook his head. "I have no idea," he admitted. "But Re seemed to know exactly what he was doing, going with her."

"Well, how do we get him out of there?" Sirius demanded. "Is there a spell to make the Willow freeze again?"

"I'm sure there is," replied James, "but none of us know it."

"Ugh. Where's Remus when we need him?"

"Trapped under a bloody tree."

The three of them crept cautiously forward, closer and closer to the Willow; one of its boughs came swooping suddenly down from the sky, embedding itself in the ground just inches away from Peter with a sickening thud.

"Merlin," Sirius whispered. "That thing's going to kill us."

Peter whimpered. "Can we go back now? I don't want to die."

"Fine," said James, kicking at the ground in frustration as the bough shook itself free from the earth. "Stupid tree. Guess we'll just have to come back next time, and hope no one trips over anyone's shoelaces again." Peter looked down guiltily.

The boys left the Willow and returned to the castle, heading up to their dormitory to get ready for the night's Astronomy class.