The Gryffindor Common Room, Hogwarts

Percy

After Melinoe disappeared, and the oneiroi fled, the Hogwarts students began waking up. Apparently, they could not remember a thing. Maybe Melinoe did us a favor, Percy thought. Thalia was already working hard to make them sixth years, though they were older, so she had to make them all look younger while making everyone else think they'd seen them before.

For Percy, that meant Thalia didn't need to yell at him anymore, but he had more pressing issues at hand. "What are the Gates of Horn and Ivory?" he asked.

Jason scrunched up his brow. "Well, they are more like a literature definition," he answered.

"But Melinoe told me to seek them out," Percy replied. Jason shrugged.

"Who knows?" he said. Annabeth was looking at them quizzically.

"You know... I think I am beginning to suspect someone," Annabeth said, quietly.

"Who?" Percy questioned.

"Remember when the Oneiroi made everyone fall asleep?" Annabeth continued. "Only the demigods were able to stand up to that. Except someone else also did, and he is-"

"Harry!" Percy cried. "That reminds me, he asked me about gods of darkness! Do you think he is the one who impersonated Jason?" Percy asked.

"Yeah, I think so, but there's something else too. Professor Dumbledore also was able to take the hit, and we don't know if he's demigod or not," Annabeth told them.

"So you think either Harry or Dumbledore?" Piper had joined in the conversation. Annabeth shrugged.

"Probably," she replied.

"Can you see them as a descendant of Iapetus?" Piper asked, frowning slightly. "I kinda thought Luna Lovegood from Ravenclaw, though at first I thought Mnemosyne was more relevant, but..."

"Anyways, we'd better get some rest," Percy yawned. "I'm tired."

"Wait. Come back," Jason instructed. "I want to talk about something else." Percy peered at him sleepily. "Remember that room we went into?" Jason asked.

"Yeah," Percy answered halfheartedly.

"Remember what day it was?" Jason asked. Percy frowned.

"No...," he replied, scratching his head.

"It was the first day of winter," Jason replied. "And the winter solstice."

"The winter solstice?" Leo asked.

"Yeah. That's the day Hades is allowed on Olympus. It is also the darkest day, and the Olympian Council's annual winter meeting," Jason explained.

"So you're saying the room only appears on that day?" Percy asked, incredulously. "But that means we'll never-"

"No, that day is when Hades leaves the Underworld, passing another set of gates. The Gates of Erebus," Jason informed them. "The gates are left open. That might have something to do with-"

"The room's opening! So you mean the door is somehow like the gates?" Thalia asked, excitedly.

"Not exactly. They'd be related, sure," Jason replied. Annabeth was watching them.

"I propose a plan. Tomorrow, after school, Nico shadow travels to the Underworld and leave the gates open," Annabeth instructed. "Then shadow travel back, and we head to the room. Hopefully, we can find out more about how to get to Erebus there," Annabeth concluded.

"Annabeth, you're forgetting something," Jason reminded her. She blinked in surprise.

"I did? Oh, of course. Day and Aether..." Annabeth was lost in her train of thoughts.

"Day and Aether?" Percy frowned. "What-"

"Remember? Erebus chases Aether, and then Hemera, or Dies, shoos away Erebus everyday," Jason said. "If we're going to get into Erebus, we'd best do it while he's gone, at midnight."

"But we're just going to the room," Calypso added. "Surely, there wouldn't be-"

"No. The room was oddly cold, and it was all... so," Percy said.

"Got it," Annabeth replied. "So sleep well folks. Tonight, at midnight, we're going out."