Present Day

Everybody moved into the refinery, slowly and quietly, but once again nothing seemed out of place. It was perhaps a little creepy for the ghost town/refinery dynamic to be there in the first place, given just a couple of dozen miles away was one of the busiest cities in Scotland, but within the setting everything seemed how it should do. The refinery was bare, stripped of all equipment and machinery, and anything else that could be considered valuable. A thick layer of dust had settled on everything, and showed no sign of having been previously disturbed. No sign of Wyatt Munroe.
"Are we sure we have the right place?" Cable asked. "This doesn't look like it's been touched in years."
"We have the right place" Artemis said. "This is just a front. Appearances can be deceiving."
There was a brief pause, and then Artemis almost jumped straight through the roof, startling everyone.
"That's it!" Artemis said, with more enthusiasm in his voice than had ever been heard before by anybody in the room. "I know exactly what Wyatt wants to do with The Obelisk. It's so simple now."
"What is it?" Masek asked.
"Nothing good" Artemis replied. He did not elaborate. His eyes began to dart across the refinery, until they seemed to latch onto something. He began to walk towards it, not waiting for anybody else to follow. They did follow, eventually.
"What is it?" Butler asked, hovering besides Artemis.
"If something looks out of place" Artemis said. "It most likely is. This refinery was made up of several stations, all intricately connected. You can still see the connections etched into the ground if you want to. But this lever connects to nothing, it has no purpose, it shouldn't be here. And if it shouldn't be here..."
Artemis pulled the lever, and the section of the floor they were all stood on began to descend.
"How did you figure all of that out so quickly?" Masek asked.
"Superior processing brainpower" Artemis replied. "Going down..."

Artemis estimated that they were at least 100ft underground. Nobody dared to question how he'd estimated it.
"A remarkable change of scenery" Artemis said, looking over the shiny white walls and sleek metal floor.
"I wonder how long it took Wyatt to build this?" Cable asked, also looking around.
"I doubt that Wyatt built this himself. He is not an architect nor a builder" Artemis replied.
"Neither are you, and yet you construct all manner of things" Masek pointed out.
"What I do is engineering" Artemis corrected him. "This is structural architecture. There is a difference."
"Are we going to address a more important issue?" Butler asked. "Such as the fact that there are three different corridors we can go down?"
"I was about to address that" Artemis said. Butler was right; There were three identical corridors going off in different directions. All of them contained curves such that you couldn't tell what was at the end of them.
"How do we know which one to go down?" Scarlett asked. Artemis had almost forgotten that she was there; She was incredibly adept at hiding her presence. It's one of the reasons he brought her into the FRA.
"We don't" Artemis replied. "And whilst one of these corridors most likely leads to Wyatt Munroe, the other two will lead to something far less pleasant."
"That's saying something" Cable replied. He tried to keep it quiet, but everyone heard him.
"Myself and Butler will take the middle corridor" Artemis said. "The three of you can decide between yourselves how you're going to split up."
"Why the middle?" Masek asked.
"Symmetry" Artemis replied. "And if Wyatt actually wants to meet me, he'll know that. However, we have to be sure, so I need you to go through the other corridors and check. I can't guarantee what you find won't try to kill you."
"I'll take anything on" Cable said.
"Of course you will" Artemis replied. He looked at Butler. "Let's go."

As Artemis and Butler traversed the middle corridor, the sounds of the remaining FRA members fell away, and left just the two of them together, in silence.
"This corridor seems to go on forever" Butler said, breaking it. "What exactly are we looking for?"
"If I knew what we were looking for" Artemis replied. "Then I would have brought everyone with me. The fact that I have brought us here with a serious disadvantage should show you just how desperate I am to find Wyatt Munroe. You are correct, though, this corridor does seem to have an infinite value to its length, from this perspective at least. The longer I spend in this corridor, the more I am convinced that this staging post is not of Wyatt's design. He has a certain penchant for chaos that is not reflected in the architecture."
"I didn't realise that you were an architect now" Butler remarked. Despite Artemis essentially leading the charge towards Wyatt Munroe, Butler had the actual lead on the ground.
"It does not take an architect to determine that this design work is far too clean –"

SCHLINK!

Artemis should have seen it coming, but the infinitely repeating pattern to the corridor had masked the small aberration in the floor markings, where a reinforced glass panel had sat, waiting. As soon as Butler had walked past it, it sprang up, placing itself between the two of them. It had been so fast, so sudden, that Artemis had almost walked straight into it. Butler had instantly turned around, but even that wasn't quick enough, and the two of them were now very much separated. Butler pounded his fists on the panel, but it would neither bend nor shatter.
"Artemis Fowl" a voice boomed from the overhead speaker, which was 100% that of Wyatt Munroe. "I spent a great deal of time last night debating whether you were going to show up, once I knew you had located my little hideout. I'm delighted that you decided to show your face after all. You even brought along a few friends, though admittedly not the ones I had hoped for. Nonetheless, I believe it is time for us to finally end our dance in the shadows, and settle this man to man, just the two of us. What do you say, Artemis?"
As Wyatt finished, a panel in the wall next to Artemis slid open, revealing a large room beyond it. Artemis locked eyes with the man standing at the end of the room, staring him down.
"Artemis…" Butler tried to warn him, but Artemis held his hand up.
"I'm sorry" Artemis replied. "But this is the only way."
Wyatt curled his finger, beckoning Artemis forwards. Artemis took a step into the abyss, and the wall panel slammed shut behind him.
"I really hope you know what you're doing" Butler said as Artemis disappeared, then went back to banging on the glass.