I find Bill where I've always found him, practicing spells in the Training Grounds.

"Bill," I gasp. "The whole castle's frozen. We're going now." I don't wait for an answer, but take off, making my way through the frozen halls. Several times, we have to stop and melt the ice to clear a path.

Penny and Ben are already waiting when we finally reach the door. Penny gives Bill a bottle of the Fire-Breathing Potion. "Drink this. We can use it on the door."

Bill uncorks the bottle and downs the potion inside. I find my bottle in my robes and gulp it down. The potion tastes spicy, and my tongue burns as I swallow it. I hope Penny brewed this correctly, I think nervously. I don't doubt her skills, but Fire-Breathing Potions have been known to melt people's tongues if brewed incorrectly. I'm rather fond of my tongue.

I choke down the last of the potion. Abruptly, the burning sensation disappears, replaced by a minty aftertaste, as if I've just brushed my teeth. My tongue is thankfully unmelted.

Bill makes a face as he finishes his potion. "I have yet to drink a potion that tastes good," he complains.

I giggle nervously. "Come on. Let's go."

We spread out into a line as we approach the door. The plan is simple. We will blow fire at the door while dodging its freezing blasts. It's the same plan that failed Bill and I, but we couldn't think of anything better.

I blow, sending a plume of fire from my mouth. I can feel its heat in my mouth and on my face. The minty taste intensifies until it's almost unbearable. I'm grateful for it, though.

I dodge a blast from the door and blow another plume of fire. Abruptly, the snowflake starts to shudder and the blasts stop. I stand still and watch the door with bated breath.

The snowflake cracks apart and slides down. The pieces sizzle as they touch the icy landing before melting away. There isn't even a puddle. The snowflake is simply gone.

"Yes!" Penny cheers, but our joy is short-lived. From behind the door, I hear an ominous rumbling sound.

"Get away from the do-" I try to warn my friends, but before I can finish, the door crashes open. Standing behind it is a massive knight, as tall as Hagrid. Its armor is crusted with snow, and in its hands it grips a huge sword. Getting hit with that would hurt a lot.

The knight sweeps its sword back and forth. I feel cold air ripple from the blade, but nothing happens. Not to me, at least. Out of the corner of my eye, I see that Bill is now frozen in a block of ice.

"Ben, Penny, come at it from the sides!" I order. The sooner this thing is defeated, the sooner we can help Bill. "I'll attack from the front."

I blow in an attempt to breathe another plume of fire, but the potion seems to have worn off. I raise my wand. "Incendio!"

"Incendio!" Ben and Penny charge the Ice Knight from either side, attacking it with flames from their wand. I notice that the armor on its left shoulder looks a little melted from Ben's spell. Is it made of ice?

The Ice Knight turns on Penny and waves its sword again, freezing her in ice. Now it's just Ben and I.

I cast Incendio again, aiming for the melted part of the armor. Something black drips from the ruined shoulder, sizzling on the floor and releasing an acrid stench. I wrinkle my nose. What is this thing?

"Incendio!" Ben and I attack in unison, forcing the knight back a step. I can see a tiny hole forming where we've targeted. We're getting close.

The Ice Knight thrusts its sword forwards, sending a blast of energy towards me. I fall backwards, feeling like I've been punched in the stomach. Ben immediately places himself over me, standing between me and the ice knight. In the seconds it takes for me to get back on my feet and rejoin the fight, I see that Ben is shaking. He's terrified of facing down the ice knight alone, but he's still doing it to protect his friends.

The ice knight's next attack leaves Ben frozen in ice like Bill and Penny. "F-finish it, Celena!" he tells me. I only hope that I can.

I step around him, readying my wand. My whole arm is numb, and it's hard to keep my wand level. "Incendio!" I send a jet of fire not just at the hole in the knight's armor, but through it, pouring fire into its chest. It sinks to its knees, the sword falling from its grip. Its whole arm starts dripping, filling the air with that smell of burning. I don't stop until the entire arm comes off and hits the ground. There is nothing inside it. We fought a hollow suit of armor.

I give the ice knight a suspicious look, but it doesn't move. I free my friends from the ice, going in order of when they got trapped. I don't want anyone to be frozen for too long.

"You guys were amazing," Bill says.

"Great job, Ben," I congratulate him. Penny echoes my praise.

Ben looks embarrassed. "Come on. Let's see what that thing was guarding."

I push open the door, keeping my wand raised. I'm worried that the ice knight wasn't the only protection for the vault. I'm expecting another attack, but none comes.

We enter a hexagonal room with a pattern of trapezoids on the floor. The walls are lined with suits of armor. I eye them suspiciously, but none of them attack us.

In the center of the room is a glowing golden pillar. I recognize it from one of my visions. I place my hand against it. The surface feels warm, and I can feel a gentle vibrating.

I step back as the column opens, the sides unfurling like the petals of a flower. Tendrils of golden light weave around each other. Suspended in the middle are a book covered with brown leather and a broken wand.

I pull the splintered halves of the wand from the center of the column. I stare down at them in disbelief. Even broken, I recognize this wand, though it's been almost three years since I last saw it. "This is Jacob's wand," I whisper. "How did it get in here?"

"Maybe the book contains a clue," Bill suggests, taking it and handing it to me.

As soon as my fingers touch the cover, I feel a jolt of electricity. The room clouds, hidden by white fog.

"Find the other four vaults, Celena. Find my room." It's Jacob's voice.

"Your room?" I ask the empty air. "I don't understand!"

"You can't let her get there first! Hurry!" Jacob's voice rises in pitch and volume, becoming almost hysterical.

"Who is she? Jacob, you have to tell me!" I urge. "How can I stop someone I don't know the name of?"

But there is no answer. The fog simply fades away, leaving me standing in the vault with my friends.

"You heard him, didn't you?" Ben says, his eyes full of understanding. "Your brother."

"Yes." My voice sounds hoarse. I swallow. "He told me to find the other four vaults and his room, and he warned that we have to do it before 'her'."

I open the book, hoping that it contains a clue that will help me puzzle out the meaning of Jacob's words. Instead, all I see is bizarre scribbles and drawings of things I don't understand. I sigh in disappointment. "I'll ask Rowan to take a look at this. Maybe it's written in code."

I slip the pieces of Jacob's wand into my robe pocket along with Alana's clover. The book won't fit, so I keep it in my hand. "Come on. Let's get out of here."

"You guys go on ahead. I'll hide our footprints," Ben says.

"All right." Bill, Penny, and I leave him alone in the corridor. Bill leaves to return to the Gryffindor common room, but I walk with Penny to her common room. The ice is gone. I had forgotten what this part of the castle looked like without it.

"Don't you find it a little suspicious that Ben knows so much about hiding evidence?" Penny whispers.

"He said he's been researching Concealment Charms," I reply.

"Yes, but I was thinking… what if he learned them before that?" Penny looks at me meaningfully.

"You think he learned them from R? You don't think he's working for them, do you?" I can't believe Ben would lie to us. I don't think his amnesia is faked.

To my relief, Penny shakes her head. "No. I think Ben is done with R. But that doesn't mean that they're done with him."