Because they were busy playing with the dog, by the time Kael and Cedric arrived at the Three Broomsticks, everyone else was already there.
Once they sat down, Fred pushed two bottles of Butterbeer to them, curiously asking, "Exactly how much did you buy, you took so long."
"If you were any later, we were about to come look for you two."
"Not much," Cedric said, "but on our way out, we found a very interesting big black dog, which delayed us a bit."
"A black dog..." George frowned and muttered softly, "Could it be... bad luck?"
"It should just be a stray dog from outside that wandered in accidentally." Cedric said, "Or maybe it was brought by a customer from the Hog's Head Pub, Devis Shop is right next to the pub."
"Probably," Fred nodded, "All kinds of people go there. Last time George and I saw someone stuff a five-foot-long bone into their robe."
"We guess it could belong to a Troll..."
"The smell was really disgusting..."
Fred put down his cup, "We used to want to go in and take a look, but after that we temporarily gave up on the idea."
"Because of the Troll bone?" Cho asked.
"No, because we got kicked out by the pub owner." George shrugged, "That old guy has a terrible temper..."
They chatted while drinking Butterbeer.
Later, when Kael passed by Devis Shop again, the black dog was gone, and it never appeared again until the end of the visit.
At the appointed time, everyone followed Professor McGonagall back to the castle.
Kael didn't even go back to the common room, he directly ran to the Room of Requirement on the eighth floor, and the others followed.
Previously Cedric had mentioned the Mist Gem, and everyone was very curious.
Coincidentally, Kael was also preparing to test its effects, so they simply tagged along.
"I need a very large room, with wind blowing."
Kael paced back and forth in the hallway three times, and a door appeared.
They walked in, and immediately a strong wind blew them off balance.
Conna was almost blown away, fortunately, Kael grabbed her just in time.
"The wind here is too strong... you should have specified a bit more..." Fred shouted, his voice barely carrying over the noise.
"We're here already... let's just go with it... besides, a bit of wind is good..."
Kael didn't plan to continue going forward, he reached into his pocket, took out a Mist Gem, and crushed it.
The fragments began to dissolve, transforming into large clouds of dense mist that spread around them.
In just a few seconds, they found themselves in a hazy, white world.
The howling wind was gone, seemingly blocked by the dense fog.
Fred rubbed his eyes and realized he could now only see George, who was closest to him, and a faint shadow of Cedric.
"No wonder it's worth twenty Galleons..." George's voice came from beside him, "Kael, where are you?"
"Here." Kael and Conna walked over, with Cho and Cedric following them.
"Amazing..." Cedric marveled, "The wind that almost blew me away is actually blocked by this fog..."
"You get what you pay for." Fred chuckled, "This thing is twenty Galleons... if a bit of wind could blow it away, Kael could go demand a refund from Devis."
"Let me try another." Kael took out his wand.
"Scourgify!"
"Aguamenti!"
"Incendio!"
...
Kael constantly switched between different spells, but the dense mist showed no sign of change, or if it did, it quickly returned to its original state, maintaining a visibility of less than a meter.
George also tried a few spells, curiously asking, "Kael, how big do you think this area is?"
"I don't know." Kael shrugged, "The shopkeeper didn't say."
"How about we test it?" Fred suggested.
Everyone agreed to the idea without hesitation.
With nothing better to do, Kael conjured a long rope with his wand and tied it to the door handle, then, together with everyone else, they followed the patterns on the floor forward.
Half an hour later, they stopped in front of a wall.
"Is this the end?"
Kael touched the wall and changed direction.
This time, it was quicker; it only took them a bit over ten minutes to stop again.
Kael realized, somewhat embarrassingly, that he had underestimated the extent of the fog.
He had only asked for a very large room, but even the largest room has an end.
"In retrospect, I should have said something even bigger, like a forest..." Kael tapped his forehead.
With no other choice, they followed the rope and began to head back.
"At least now we can confirm that the Mist Gem has quite a range."
Fred said, "Even though we walked really slowly, in half an hour, we must have crossed at least five Quidditch pitches."
"Eight..." Cedric said, "I'm certain."
George grinned, "Imagine, if during a Quidditch match we threw one onto the pitch, what would happen."
"That would be interesting." Fred laughed, "They wouldn't be able to see people or goals, and as they flew, they'd suddenly realize they were already in Hogsmeade."
"Perhaps they could go to Honeyduke's Sweet Shop and see if they could find raspberry-flavored Golden Snitches."
"Kael, you really should give it a try..."
After saying this, the two of them laughed even harder.
"Whether Honeydukes has Golden Snitches, I don't know, but I do know I'd be out twenty Galleons."
Kael glanced back at them, "And I might end up in detention with Professor McGonagall."
"That's true..."
Fred sighed, "Detention isn't the problem, but twenty Galleons is really expensive."
He reached out as if trying to touch the mist.
They returned to the door and waited for a while... a breeze suddenly blew across them.
Soon, the wind picked up, and the mist began to slowly dissipate.
"It should be about right now."
As their robes started billowing in the wind, Kael opened the door and walked out.
"Exactly two hours." Conna checked the time.
"Two hours, twenty Galleons... that's a pretty expensive tool," Fred clicked his tongue.
"Just thinking about it now makes my heart ache a bit." George said, "Twenty Galleons could buy ten boxes of Stink Pellets, enough for a whole school year."
"A whole school year with ten boxes of Stink Pellets?" Fred exaggerated, "If we really used that many, I guarantee Filch would kill us."
"Then stretch it over two school years..."
"Wait!" Suddenly, Cho seemed to remember something and asked, "What time is it now, isn't the Halloween feast already..."
"Oh no!" Conna realized, exclaiming, "It's seven ten... the feast started ten minutes ago!"
...