So Proboscis had actually been Pinkie Pie all along.
Labrum chuckled to himself as he headed down to the lowest levels of the hive. He had known bringing her along would be fun, but he certainly hadn't seen that one coming.
The chuckle turned into an wholehearted laugh as his new mission led him through a static hole into a long underground tunnel. It took him several minutes of trotting through the tunnel – it was too small to comfortably fly in – before he reached his destination.
Just below the edge of the wasteland surrounding the hive, the tunnel opened up into a room containing a changeling guard and what he needed.
On the close side of the room, a disheveled, skinny unicorn mare sat behind iron bars. An empty cell next to hers came further forward, stretching just barely across where the boundary of the wasteland would be.
Normally prisoners would be cocooned, but Gateway required special arrangements.
Her orange fur was covered in bloodstains from the beatings it had taken to make her cooperate, and her dark mane was all messed up. The maneband that had held her ponytail in place was gone, and of the white and black-striped socks she had been wearing when Labrum first met her, only one remained on her front left hoof. Her white tank-front shirt had seen better days, too.
Gateway looked at him with apathy in her half-lidded eyes. She had fallen far from the enthusiastic traveler she had once been.
Labrum smiled at the sight. He and Clypeus had done a good job, capturing this one.
"I need to go to Canterlot," Labrum told Sclerite, the guard on Gateway duty. "Queen's orders."
Sclerite nodded and pulled a latch that opened a gate between the two cells. "You heard him," she told Gateway harshly.
Gateway slowly got up, wincing in pain at some ache or other, and trotted over to the other cell. She stuck her horn out between the bars, and it lit up.
Unicorn magic could not function within range of the Queen's throne, but by placing Gateway at the edge of the effect, the changelings had managed to give her access to her spell whenever they needed it, and in such a way that she couldn't use it within her cell.
A circular hole appeared in the air in front of Gateway. Looking through it, Labrum could see another location entirely. It wasn't Canterlot, though.
"Maggot," Sclerite swore, looking through the hole to see the dark room filled with cages holding chimeric monsters. Some of them looked back at the changelings. "That's Tartarus! Quit playing around, or you won't get food for three days."
"It's where he should go…" Gateway mumbled, but obediently closed the hole and lit her horn anew, concentrating.
Nothing happened.
"What's taking you so long?" Sclerite demanded.
"It's… it's not working," Gateway said, surprise breaking through her apathy.
"What?"
"It's not working!" she repeated. "It's like there's something blocking me."
"If this is a game, you're in for a beating," Sclerite threatened. "Try harder."
"I am trying harder!"
"What about somewhere near Canterlot?" Labrum suggested. "I can fly the rest of the way."
Gateway concentrated, and a hole appeared. This time Labrum could see signs of Canterlot architecture, and it wasn't even all that far away. Gateway could have put him in Ponyville, but as far as he could tell, the hole was on the side of Canterlot Mountain, near the railway.
It would work.
"Thank you," he said to Sclerite, then slipped through the hole.
On the other side, the mountain chill bit at his exoskeleton, so Labrum shifted into a thick-coated pegasus and took off towards Canterlot, leaving the hole in the air behind him. When a changeling went through like this, the guard on duty would generally have Gateway leave the hole open until it closed on its own after about ten minutes, just in case something went wrong.
By coming up along the railroad, shielded as it was from the worst of the wind, Labrum would avoid suspicion. To anypony who saw him, he would appear simply as a pegasus who had decided not to pay for railroad tickets in favor of flying himself. Case in point, he could see another such pegasus flying behind him.
He made the last turn, and there it was, Canterlot Ci—
Bonk.
Labrum rubbed his forehead. What the buzz? Laughing nervously, he put his hoof forward in the thin air and hit something hard.
From behind him, the real pegasus caught up and flew past him into the city. Labrum tested the spot where she had passed through, to no avail.
Something invisible was keeping changelings out of Canterlot.
"Psst! Hey, over here!"
Labrum turned his head towards the sound, which had come from a nearby bush. Upon closer inspection, he could see an undisguised changeling hiding in it. Well, things were strange enough already.
He landed and tried to approach the bush, but the barrier kept him from getting closer than three pony lengths.
"Elytron?" Labrum said, recognizing the spy. "Why aren't you disguised? What's going on?"
"You just found the reason face first," Elytron said. "That barrier isn't just keeping you out and us in, it's also messing up changeling magic within it. Ommatophore and I have been stuck in our base forms ever since it went up. We're lucky we weren't in public when it did."
"Yikes," Labrum said. That would have been a disaster, and this was bad enough as it was.
Elytron hesitated. "Um… You're Labrum, right? No other changeling I know laughs like that."
"Yeah. Didn't the Queen send word that I'd be coming?"
"Communications in and out of Canterlot are busted too. I thought the Queen knew about that."
"So who's doing this? Shining Armor? I thought his shield spell was a lot more… blunt."
"Well, yes and no," Elytron said, "It's not so much a who as a what. It's an artifact, made by Shining Armor, his sister, Celestia's master artificer and Thorax – we didn't know it was Thorax or what they were doing until it was too late. We've tried to get close enough to do something about it, but it's hard when our forms are stuck like this."
"Yeah, I can imagine."
"What are you doing here, anyway?" Elytron asked.
"Get this," Labrum said with a laugh, "We found Pinkie Pie in Manehattan and she just followed us right back to the hive, pretending to be a changeling! So now the Queen wants me to take her place here."
"Wait, what? Labrum, Pinkie Pie has been here in Canterlot for weeks. I saw her thirty-two minutes ago."
"What? Then who…"
"I don't know, but it's not Pinkie. Unless she can be in two places at once, which I honestly wouldn't put past that mare."
Labrum sat down, and burst into one of the biggest fits of laughter he'd had in a while. None of this was funny. It was a serious obstacle to his mission, to the Queen's plans. He would have to return to the Queen with news of failure. He knew that!
But buzz if he had expected any of it, and for that, he laughed.