After the Easter holidays (Eren, Armin, and Mikasa had gone home again), they began noticing that Reiner, Bertholdt, and Annie were skipping classes. Armin asked his friend Marco to watch Bertholdt because they were both in Hufflepuff, and Mikasa asked Jean to watch Annie. Even with both Jean and Marco helping them, they still didn't find anything out about Reiner's, Bertholdt's, and Annie's disappearances.

Exams were quickly approaching, and Mikasa and Armin were slowly getting ever more insistent that Eren needed to study a lot if he wanted to go on to the second year next year. Armin suggested that maybe Reiner, Bertholdt, and Annie just wanted some time for the three of them to spend together alone. Maybe it wasn't suspicious at all.

Exams weren't really as hard as Armin and Mikasa had made them out to be, Eren thought after his first day of tests. He'd just needed to remember the names of a few spells, a few famous wizards, and what the different herbs looked like and what potions they were used for. He hoped that it just hadn't seemed easy.

Their potions teacher had made friends with Eren, and he was often drunk when he wasn't supposed to be. Eren would tell him it would get him fired, but he didn't listen. He also insisted that his students call him "Hannes" rather than by his last name (which he refused to tell). Eren wasn't worried about his grades for potions, because Hannes usually gave him a perfect score no matter what he did.

The night exams were finally over – they still had the quidditch championship and the end of year feast to look forward to – Eren noticed Reiner slip out of his bed when he thought everyone else was asleep.

He called Mikasa's name up the stairs to the girls' dormitory until she got up to see what was going on (he had already tried climbing the stairs earlier in the year).

"What's going on?" she asked.

"Reiner's on the move," said Eren. "We need to get Armin."

They walked over to the Ravenclaw tower.

"I have holes in my top and bottom, my left and right, and in the middle. But I still hold water. What am I?" asked a statue of an eagle above the door to the Ravenclaw common room.

"Uhhh," Eren had no idea. Anything with that many holes couldn't possibly hold water. He imagined a fishbowl with that many holes.

Mikasa thought for a minute. "Is it… a sponge?" she wondered.

"Correct," said the eagle. The door below it opened to reveal a large room with lots of furniture of every shade of blue. Eren ran up the staircase that would be to the boys in Gryffindor, but it turned into a slide and he slid down.

"Wrong one," he muttered. He ran up the other one, and peered around cobalt-curtained four-poster beds until he found Armin sleeping with his face in a book about dragons on his pillow. Eren reached out and shook Armin's shoulder.

"Armin," he whispered. "Wake up."

Armin lifted his head heavily and peered through his eyelids at Eren.

"What are you doing here?" he asked.

"We have to follow Reiner," said Eren, realizing how futile this sounded now. Reiner was probably long gone by now.

"Eren…" Armin sounded exasperated. "Who let you in?"

"I know how to answer riddles!"

"Yeah, but who let you in?"

"…Mikasa."

"OK, just give me a sec."

Armin pulled on a bathrobe and slippers and picked up his wand from the bedside table. "I'm ready."

Eren and Armin met Mikasa in the common room and the three of them took the shortest route they knew to the spot where Reiner usually met Bertholdt and Annie.

Reiner and Annie stood in the shadows under a suit of armor, only visible because of their blond hair. Bertholdt obviously wasn't there yet.

Quiet footsteps pattered down the corridor as Bertholdt ran around the corner to Reiner and Annie.

"Sorry, Marco didn't want to let me leave," he said. "So do we have access to the brooms?"

Annie nodded.

The three of them left through the door Eren, Armin, and Mikasa had strategically placed themselves next to.

The three of them picked out brooms and walked over to the wamping willow nearby. Eren watched as the willow froze and each of them climbed into a hole in the ground underneath the roots.

"Why would they need brooms underground?" Mikasa wondered aloud.

"They probably don't want Filch seeing them flying away from the castle," said Armin. "The hole probably comes up somewhere."

The willow unfroze as they approached. As Eren tried to slide under the wildly swinging branches, Mikasa tackled him. The branch that was coming towards his face passed right over them.

"How did they get the tree to freeze?" asked Armin.

"I don't know, I didn't see," said Eren.

Mikasa shrugged, letting Eren up. She had still been in the broom shed when Reiner, Bertholdt, and Annie had gone under the tree.

"Then we need to find a different way of getting around it," said Armin.

A branch flew out of nowhere and wrapped itself around Eren and Mikasa, lifting them into the air above the tree. Eren and Mikasa struggled, pounding the wood gripping them with their fists and trying the few spells they knew.

"Armin! Do something!" called Mikasa.

Armin muttered, pacing around below them.

"How do I kill a tree?" he asked them.

"I don't know – Fire! Light a fire!" answered Eren.

Armin muttered an incantation, and blue flames erupted from the end of his wand. The flames caught on the tree trunk, and the tree was forced to drop Eren and Mikasa to pat out the fire. While the tree was preoccupied, the three of them opened the trapdoor by the roots.

Through the trapdoor was a sloped tunnel that was too steep to climb down and quickly went out of sight. They would have to slide down.

"Who's going first?" asked Mikasa.

"I will," said Eren. He stepped forward and lowered himself into the hole. "See you at the bottom."

Cold air rushed by him as he sped down the steep tunnel. After close to a minute, he was spat out into a chamber with walls painted in runes.

"It's OK!" he called up the tunnel, hoping his friends could hear him.

Soon after, Mikasa landed next to him, followed by Armin.

"Those runes are Thorn and Haegl," said Armin when he got his bearings. "Pain and destruction. We need to get out of here."

"They're just runes," said Mikasa. "They won't really cause pain and destruction."

"If muggles draw them. If a wizard or witch draws them, they can have serious consequences. Whoever drew these didn't want anyone to live very long after they got out of here."

"Either way, we need to find Reiner, Bertholdt, and Annie," said Eren, trying to get his friends' minds back on track.

They walked down the hall for a bit before it sloped upwards in a gentle slant.

"Why couldn't they have just made the tunnel flat?" Eren wondered aloud after probably a mile of upward-sloping tunnel.

"We probably went under the lake," said Armin. "See, the ceiling is moist and we're down far enough."

"If we hurry up, maybe we can catch them," suggested Mikasa.

The three of them broke into a jog. Soon, they came up to the end of the tunnel. They stepped out onto a field in the middle of nowhere and looked around. Lights flashed near the horizon the left.

"They're probably somewhere over there," Mikasa pointed to the lights.

So this is what they needed the brooms for. Eren, Armin, and Mikasa mounted their brooms and flew in the direction of the lights.