Winter's End is behind them, and the next sign over the door reads "Brown Crystal," "Area: Helician Labs" and "7 Emeralds." The counter starts at Scoti 72, Basket 71. They have two emeralds left over from the last level, which one of them takes as a sign they got all of those.
Packing for time travel
Right inside, a warning: "Time travel can cause intense nausea and headaches." That changes the plan. If they're about to get sent somewhere they can't get back from, they want their stuff first. So it's back to base for an enchanting table, lapis, an anvil, leather "in case we need some really crappy armor," a pile of blocks, the pig spawner and some grass for food. "Paranoid maybe, surviving for sure."
The first teleport doesn't make anybody sick. There's fire on the floor where they land, and a button they read out as "back to intersection four." So they put most of it in a chest instead. "We're gonna put all this down, and then there'll be a second teleport." They keep a fortune pick, just in case.
The labs
The place is full of redstone and daylight sensors. One of them flips every switch in sight while the other one fights, on the theory that eventually one of them will be a trap. A journal they find describes "a prototype of a mobile... electro turret for military applications," and the writer swears they'd never steal it for "their private army of unstoppable death machines." Not for a moment.
The mobs are new. There are "beacon guys" with guardian beams, coming from guardian spawners set into the walls, and guys carrying potion bottles that turn out to drop experience bottles, so they try to keep that spawner alive. Then archers with dispensers on their heads show up with fire bows. A spawner in the ceiling rains harming potions on them, and it gets crowded fast. "I was starting to get beat up real bad."
Down the chute
Downstairs there's a chest with instant health, strength and speed potions, plus one they read as an "adrenaline potion." More mobs come down a chute from a spawner above, so they block it off. A second chest has fire protection, a regeneration potion and a diamond axe. "Diamonds are for Scoti."
One of them breaks a spawner and worries it was the experience bottle one. It wasn't; the other one saved that one down below. One mob takes forever to kill. "My sword is awesome and my strength buff doesn't do anything."
A Lightning Trap
A sign on the way mentions "first floor robotics." Past a lava pool, which they put out, there's a diamond block to mine and a Lightning Trap. The tooltip says mobs near the trap "are struck by lightning," and the potion isn't used up when thrown. "We haven't had a lightning trap yet, have we?" They haven't. By now Basket's inventory also holds a Mechanical Chestplate with Protection III and Blast Protection II.
They kill one more mob and the spawner it came from, and leave the elevator shaft for next time. A sign there lists what's on each floor, nuclear core included.
Nobody dies, so the counter still reads 72 and 71. The monument isn't shown, and no emeralds turn up yet, so emerald blocks stay at 8 of 12.