Grace had never been much of a planner, preferring to react to things as they happened. Fortunately, Rowan was meticulous about everything she did, so most of the planning became her responsibility.

Grace, Rowan, and Ben met in the Artefact Room several times a day to discuss how to get behind the locked door.

"Aren't you scared of what you'll find behind the door?" Ben asked one day. "You don't know what kind of power the Ice Knight has."

"I'm sure it won't be anything too bad. Nothing we won't survive, at any rate," Grace said soothingly.

Ben didn't seem particularly reassured. "I think I'll stand guard, if that's all right with you," he said. "That way I can go for help if you get into trouble."

"That's a good idea," Grace decided. She nodded at Ben, who visibly relaxed.

Rowan scribbled down ideas on a piece of parchment.

"The door's bound to be protected somehow. We need to take a look at it and find out what we're dealing with," she said.

Grace frowned. "Merula's a light sleeper. I don't think I can leave the dorm without her noticing."

"Badeea's also a light sleeper, but I doubt she'll care if I leave," Rowan said. "I'll go up there tonight."

Ben opened his mouth as if he was about to say something, but then closed it.

...

That night, Rowan lay awake in her bed as her roommates drifted into sleep one by one. When she was satisfied that the other girls were fast asleep, she slid off her bed, grabbing her wand and glasses off the nightstand beside her bed. She shoved the glasses onto her nose and gripped the wand in her hand.

Slowly, she crept past the line of beds, cursing the fact that her bed was the farthest from the door. Once, she thought she heard Badeea stirring. She froze and listened closely. She heard nothing but the sounds of deep, even breathing coming from every bed.

She padded silently down the spiral staircase to the common room. While Badeea wouldn't have cared if she'd woken and seen Rowan leaving, sneaking out of the common room in the middle of the night was sure to attract suspicion if anyone saw her.

She scanned the common room, concealed in the shadows of the stairs. The coast was clear.

Her heart was pounding as she left the common room. She felt a rush of excitement. This was just like in The Howling Forest, when Ariadne snuck out of her aunt's house to find out what her cousin was doing.

That escapade had revealed that Ariadne's cousin was a werewolf, and Rowan would get answers from her own midnight venture.

Her courage faded, just a little bit, as she walked through the deserted corridors. Filch and Mrs. Norris lurked in every flickering shadow, eager to get her in trouble. Every tiny noise was caused by Peeves; he, too, would end her adventure.

She gripped her wand tightly, fighting the urge to cast Lumos. She couldn't risk the light giving her away.

Her nerves only grew stronger the closer she got to the locked room. Surely she would find its guardian soon.

Finally, she reached the corridor where the locked room was located. She peered around the corner, her eyes just picking out a small, feline shape in the dim corridor.

Mrs. Norris. That would explain why Rowan hadn't seen her in the corridors recently.

She couldn't get any closer to the door without Mrs. Norris seeing her. They'd have to find a way to prevent Mrs. Norris from going to Filch while they snuck into the locked room.

The next morning, Rowan reported her findings to Grace and Ben in the Artefact Room. They'd continued eating in the little room even though Merula had been leaving them alone, since they needed to discuss their plans.

Rowan pulled out a piece of parchment and laid it on the floor. She also pulled out a quill, which she fiddled with as she spoke. "So what we need is a way to get Mrs. Norris away from the door, a way to ensure Filch stays away, and a way to unlock the door," she said, listing the three items on the piece of parchment.

"Professor Flitwick said that we'll be learning the Unlocking Charm next week," Ben said.

Rowan nodded and scribbled Unlocking Charm next to where she'd written How to unlock door.

"I bet Tulip would be willing to help distract Filch. We wouldn't even need to tell why we need her help, she loves pranks," she suggested.

Grace frowned. "But wouldn't that mean we'd have to go during the day?"

"Not necessarily. I'm sure Tulip could think of something to do during the night. If not, we could always go during the next Quidditch match. Everyone goes to those- well, everyone except us." Grace had watched the previous Quidditch matches, but Rowan and Ben hadn't.

Rowan wrote Tulip's name down on the paper. "That just leaves Mrs. Norris."

They all thought hard for several minutes, but nothing came to mind.

"Ben, you have a cat, don't you?" Rowan asked suddenly.

"Ye-es," Ben said.

"Tell us everything you can remember about your cat. It might help us get an idea."

"Okay, but he's nothing like Mrs. Norris," Ben said. "He's orange, and he likes to be petted or watch birds. Sometimes he'll play, but mostly he just lies on the couch and sleeps."

"That's it!" Rowan interrupted. "Sleep! We need Mrs. Norris to sleep!"

"And I think I know how to do it," Grace said. "Penny Haywood told me to ask her for help with potions if I ever needed it. I'm sure she knows a potion to put a cat to sleep."

"I doubt this is what she had in mind," Rowan said, but she wrote Penny's name down on the paper.

With their plan complete, the three of them dispersed to their first classes of the morning.

...

Slowly, the pieces to their plan fell into place. They paid careful attention when Flitwick taught the Unlocking Charm, Alohomora, in class. Grace and Ben exchanged a grin across the aisle when Flitwick awarded Ben five points for casting the best Alohomora of anyone.

Tulip agreed to keep Filch distracted without hesitation. She told Rowan that she'd been looking for an excuse to prank Filch.

All that was left was for Grace to seek Penny's help, but that was proving harder than she'd anticipated. Penny was never alone, and Grace could never find a way through the group of students, not all of them first-years, that hung around her like a perpetual cloud of perfume.

Finally, an opportunity arrived. Penny hung back after one of their Herbology classes, and told her friends to leave without her. The two Hufflepuff girls left.

Grace waited at the entrance to the greenhouse while Penny talked to Professor Sprout. She couldn't hear what they were talking about, but Penny looked happy when she left.

"Hi, Grace!" Penny said cheerfully as she walked out of the greenhouse.

"Hi, Penny. Listen, I need to ask you for something. A favor," Grace said.

"Of course. What is it?"

"Do you know any potions to put a cat to sleep?"

"A simple Sleeping Draught should work. But why do you need to put a cat to sleep?" Penny asked.

Grace hesitated.

"I'll find out eventually, you know. I hear about everything that happens at Hogwarts," Penny said matter-of-factly.

"All right. It's for Mrs. Norris. I want to sneak into a room that she's guarding."

"The forbidden room on the fifth floor?" Penny asked.

Grace nodded.

"I'll help you on one condition," Penny said. "I want to come with you."

Grace hesitated. "I have to ask Rowan and Ben."

Penny nodded, as if she'd expected Grace to say that. "Meet me in the Potions classroom after dinner and give me your answer."

Rowan and Ben readily agreed to Penny's request.

"They said you can come," Grace told Penny when she walked into the Potions classroom.

Penny was seated at the one of the tables with her cauldron. She'd already gathered a variety of ingredients.

Grace sat down across from her.

"This is so exciting!" Penny said as she started brewing. "People always come to me for gossip, but no one ever invites me on an adventure."

Technically Penny had invited herself, but Grace didn't point that out. Instead, she watched as Penny started brewing. The Sleeping Draught was more complicated than anything they'd brewed in class so far. "Have you brewed Sleeping Draught before?"

"No, but I've brewed several of the second-year potions already, so I know I can do this one," Penny said. She dropped some sort of root that Grace didn't recognize into the cauldron.

"You don't need to stay," Penny said after a few minutes. "I'm going to be here for a while. I want to brew another potion to bring with us."

"Meet us when the Quidditch match starts tomorrow," Grace told her. They'd decided to go during the day partially because that was when Tulip agreed to pull her prank, and partially because it meant Grace wouldn't have to try to sneak past a sleeping Merula.

...

The next day, it was finally time. As everyone else was leaving the castle to watch the Quidditch match, Grace met Rowan, Ben, and the Artefact Room. Ben had his wand out and was feverishly practicing Alohomora, even though he'd mastered the spell.

"Do you have the Sleeping Draught?" Grace asked.

Penny nodded and held up a vial of lilac-colored potion. "I mixed it with some milk. That should convince her to lap it right up."

"Good thinking." Grace reached into her robes and pulled out her wand. "Are we all ready?"

Rowan and Penny drew their wands as well. They both look excited. Ben's face was grim, as if he was heading to his own execution.

Grace led the way to the fifth floor. As they rounded the final corridor, she saw Mrs. Norris sitting in front of the door, licking one paw and then drawing it over her face.

Penny took the lead. When she got close to Mrs. Norris, she tilted the vial of Sleeping Draught, pouring its contents onto the floor.

Mrs. Norris hissed at Penny, but she approached the Sleeping Draught and lapped at it suspiciously.

Her reservations faded and she began purring loudly and furiously lapping the remainder of the potion. It was the first time Grace had heard her purr.

It wasn't long before Mrs. Norris was lying on the floor, fast asleep, next to a much smaller lilac puddle.

Grace gave Penny a high five. "Nice work," she said.

"Thanks," Penny replied.

Ben stepped in front of the door and raised his wand. "Alohomora."

There was a soft click.

Ben stepped aside. Grace put her hand on the doorknob.

"Stop!"

Grace spun around, recognizing the voice instantly. "Merula."

Reflexively, she lifted her wand. Ben looked at her, and then did the same. Rowan slowly lifted her wand. Penny looked uncertain.

"Let me in that room," Merula demanded.

"Not a chance," Grace said.

"If you don't, I'll get one of the professors and tell them what you're doing," Merula threatened.

Grace laughed. "There are four of us and only one of you. I think we can stop you easily enough."

"And then when I turn you in later, you'll get in trouble for dueling as well as being out-of-bounds."

Grace sighed. "She's not going to back down unless she gets what she wants."

"No. I'm not," Merula agreed. She strode forward, pushing Grace out of the way and opening the door.

Grace grabbed the door before it closed and followed her in. Penny and Rowan also entered the room, while Ben stayed in the corridor, as they had agreed.

Grace's eyes widened as she looked around. The floor, ceiling, and walls were coated in a layer of frost, obscuring the runes Grace knew were carved into the wall. Stalactites of ice hung down from the ceiling.

She became aware that her feet had gone numb and felt very heavy. When she looked down, she saw that her feet were encased in a block of ice that was slowly spreading up her legs.

"Flipendo!" Grace said, pointing her wand at the ice. It shattered. She started pacing, hoping to keep the ice from grabbing her again.

"Grace!"

She looked over to see that Rowan was trapped in a block of ice that reached up to her waist. Her spells were barely affecting the ice- she had never been as good at Charms as Grace or Ben.

"Flipendo!" Grace cast again, and the ice encasing Rowan shattered.

Rowan turned to Penny and started helping her get free from the ice. Grace was about to help Penny when she heard a plaintive voice.

"Help."

She could hardly believe her ears, or her eyes. Merula was encased in a block of ice that came up to her shoulders and pinned her arms to her sides. Her wand was lying at the base of the pillar- she must have dropped it at some point.

Part of Grace wanted to leave Merula trapped in the ice, as revenge for all she'd done that year. But it was a small part, and Merula looked so pitiful trapped in the ice.

She sighed and raised her wand. "Flipendo."

Part of the ice cracked and fell to the ground. It took several spells before Merula was completely free. Grace made sure to aim her last Flipendo directly at Merula instead of at the remainder of the ice.

"Owww..." Merula whined as she fell and landed on her back.

"Hurts, doesn't it?" Rowan said in a satisfied voice.

Merula glared at her as she got to her feet. "Let's just get out of here."

Grace turned around and realized that getting out wouldn't be easy. While they were freeing themselves, ice had spread over the door, sealing it shut.

They were trapped.

"Flipendo!" Grace cast. Ice broke and fell to the floor, but more grew in its place.

She was aware of the others casting alongside her, but they couldn't make a dent in the ice blocking the door.

She stopped casting Flipendo. "It's no use. The ice is regrowing faster than we can destroy it."

"If only we knew Incendio..." Rowan said mournfully, looking at the door.

"I have an idea," Penny said. She pulled a vial from her robes, uncorking it and draining the contents in a few quick gulps.

"What is that?" Grace asked.

"Strengthening Solution. I thought we might need it," Penny said. "Everyone stand back."

Everyone stepped away from the door. Penny reached through a gap in the ice. She hooked her fingers onto the handle and pulled hard.

At first it seemed that nothing was happening. Then there was a great creaking sound and the door came free in an explosion of ice crystals.

The four girls left the room, entering the corridor where Ben was waiting for them. Grace's relief quickly turned to disappointment. They were freezing, Penny in particular was covered from head to toe in shimmering ice particles- and they hadn't found anything.

"I should have known better than to follow you losers," Merula sniffed. "I'll find the real Cursed Vaults by myself."

She strode away with her head held high. Grace glared at her retreating back.

"Do you think she's right?" Rowan asked quietly. "About that not being a Cursed Vault?"

"I think she is," Grace said. She felt sure that the Cursed Vault was behind the door guarded by the Ice Knight.

"We've got to get back to our common rooms. The Quidditch match will be ending soon," Penny said with a note of panic.

Grace took the lead, running through corridors and down stairs. Abruptly she halted at the top of a staircase, and Ben ran into her.

"Oh no," she breathed.

Professor McGonagall was standing at the bottom of the staircase, and she did not look happy.