I was so excited to give my idea a try that I hardly complained at all about Cluma 'encouraging' me to fight the centipedes. I wiped out the nest with lightning, grabbed an uncut sapphire from the chest, then teleported out of the dungeon. Floor eleven could wait.

"Why are you so excited?" complained Cluma. "And it's no good you thinking up a way for me to beat the hydra if you don't tell me what it is!"

"It might not work. I need to try it first."

Should I go to the institute? On the plus side, responsible adults with higher skill levels. On the other, I didn't have any concrete plans for how to level my new skills, and doing it myself was a great opportunity to earn skill and class levels.

I could start off safe. Small batteries with the feeder attached at one side instead of wrapping the battery in a shell. It would make more of a firecracker than a grenade. Then I could gradually scale up. And if, at any point, it looked like I was getting in over my head, I'd go hat-in-hand to Grover again.

"Try what?" asked an exasperated Cluma.

"To make magical explosives!"

While I'd promised Erryn not to make Earth weapons, in some ways the promise was unnecessary; I had no idea how to make gunpowder, or other conventional explosives. I could think of plenty of materials that could burn, and I had a rough idea how to make thermite, but to make something suitable for a grenade, or a bullet? I didn't have a clue. The ingredients for black powder or gunpowder weren't things I'd ever looked up on Earth, so I'd need to work it out from first principles from high-school chemistry. It was possible this world, with its complete lack of mining, didn't even have the required materials. It certainly didn't have aluminium for thermite.

Perhaps the textbooks we'd gained from Earth would change that soon...

"Huh? An explosion spell? I'm pretty sure I can't do that with my affinities."

"No, not a spell. You know how these lightning gloves have a maximum depth at which they can operate before they overload?"

"Yes? Oh, you want to deliberately overload something! How would that work? How do we get it to the hydra without it exploding prematurely? Even if you tuned it to a precise mana density, it would blow up as soon as you entered floor twenty. Ah, no, obviously, you just need to shield it from the ambient mana. Store it in an item bag? I'm not sure if they block mana... You could coat it in a dungeon stone shell, and crack it immediately before throwing it."

"Yes, that's exactly right," I said, the wind somewhat taken out of my sails by the way she'd spontaneously worked out most of my idea on her own. Whatever our stats may say, I didn't have her beat in the intelligence department; I simply had more memories to draw on. I hadn't even considered using dungeon stone for the shell, but it would work without additional enchantments, and would be easy to crack open without damaging the contents. It would be impossible to manufacture, though. How would I make a stone sphere that didn't leak mana, but still get the explosive component into it? I'd probably need the [Join Stone] skill. She hadn't come up with the idea of mixing projectiles in with the bomb, either.

To be fair, nor had I. I'd simply read the news on Earth.

"To the institute, then?" she asked.

"To Remous' smithy in the village, actually," I answered, thinking over my [Item Box] contents and deciding I had enough materials for some initial experiments. Steel was the main one, and I had plenty of that. I didn't need the mana-proof shell for the first version; I'd detonate it with [Expert Mana Control]. That just left what I needed for moving mana around. Some silver wires and monster cores would do, and I had both.

Cluma gave me a silent stare.

"I've thought through the safety, honest!" I babbled desperately, before explaining my thoughts.

"So, what you're saying is that you carefully considered it and decided to prioritise levelling over involving someone who knows what they're doing," she declared.

"I considered it, and decided doing it on my own was safe," I countered. "I have the knowledge from [Advanced Runecrafting]."

Cluma sighed. "Fine. You know the rules. You can change at your parents' house before we visit Remous. But you do remember what time of year it is, right? He might not be available."

I did not, in fact, know the rules, given that the last time it came up she'd ended up getting partially memory-wiped. Hopefully, she still only remembered the tame version. But the time of year was a valid point. Remous was dogkin, married, and not that old. Disturbing him would be risky...

There weren't any other smithies I could borrow, other than the institute. From my experience with Xander's team, I knew simply having Grover watching over me would harm my chances of levelling.

Maybe I didn't need a smithy? I could use iron instead of steel, and carve it up with an enchanted sword. Trying to fashion silver wires would be tough without a furnace, though.

The story has been stolen; if detected on Amazon, report the violation.

"Fine. We'll go to the institute. But I'm still going to do the work myself."

"Close enough, as long as you're supervised," agreed Cluma, wearing an expression somewhere between relieved and smug.

Another teleportation later, and we made our way back to the research institute. It had changed little since it was first built. A few new extensions had been tacked onto the structure as the workforce expanded, but there was plenty of space. That's why it had been built a short walk from the town in the first place. Perhaps the town would expand enough in the future that it bumped against the institute, but there was still the fenced off safety area.

An area which, now that I looked around, seemed to have redeveloped one of its original, disturbing features, that I thought had long since ceased.

"What's that noise?" asked Cluma, her ears twitching. "It's kind of... a rumble?"

I couldn't hear anything, but the sight of the twisted metal littering the fields was enough for me to leap to a terrifying conclusion from a standing start.

"Time to run," I said simply, before wrapping [Weft Walk] around us both.

"Huh?" asked Cluma as I blurred towards the building's entrance. Fortunately, she didn't hesitate, following me in.

"Phew, we made it," I muttered.

"Made what? What was..." started Cluma before the building shook, rocked by an almighty boom.

"Apparently, I'm not the only one making explosives, although I suspect theirs are accidental."

Presumably someone was trying to replicate a bit of Earth technology by some method involving lots of trial and error. Rather loud errors. What could it be? I'd soon find out, because asking for Grover revealed he was involved, and was out on one of the experimental ranges rather than in his workshop.

I found him poking at a twisted bit of metal that to me looked like all the other bits of debris, but he obviously found it interesting.

"I don't see any signs the valve failed. Looks like it worked just as we designed it."

"Too much fuel then? It's easy enough to say it should let 'some' fuel in, but how are we supposed to know how much it means by 'some'?" muttered someone else I didn't recognise.

Fuel? Valve? Were they trying to build an internal combustion engine? But we had no oil, and hence no access to petrol or diesel. Although we did have plenty of crops, I suppose, and they knew of fermentation before I got here. I'd got them started on distillation, and their textbooks likely had more information. They also would have mentioned what alcohol was.

But they were textbooks, not blueprints. They explained principles and science, not how to build things. They'd taken an explanation of an internal combustion engine, and built... well, not an engine, obviously; even if the combustion was internal to start with, it certainly wasn't by the end. But they were trying. It was all sorts of impressive.

"Want to ask for a working model in the next trade?" I asked.

"Pah," spat Grover. "Where's the fun in that?"

He stood for a few more seconds, examining the mangled valve, before his head snapped up and he spun around, finally realising who he had answered.

"Peter? What are you doing here?"

"I switched class to [Artisan]. I was hoping to borrow your furnace and tools to try a few ideas [Advanced Runecrafting] gave me."

"Oh? Like what?"

"Explosions, for a start."

"Got them covered already, lad," grunted Grover, glancing at the mess around him. Some of the grass was still smouldering.

"Deliberate explosions. Single use items for taking out tough monsters."

Grover stroked his beard as he considered that. "There's no standard enchantment for that, but I can think of a few ways to do it. None would be cheap to make, though. Seems a bit of a waste to make something that cost more than the value of the monster you killed with it. Especially since the monster wouldn't be in great condition afterwards. I can't even suggest people keeping one on them for emergency use, because any mechanism I can think of would have too great a chance of detonating accidentally."

Well, damn. Grover could think of several ways. And yes, the problems he mentioned were all real. You wouldn't want one of these on your waist, then to get knocked into a wall and have the shell shatter. There was probably some way to ensure accidental damage would also break the charging mechanism, but that would make it even more complex and, hence, expensive. If it was me, I could just hide it safely in my [Item Box], but most people with [Item Box] wouldn't be in a dungeon.

Or at least, that used to be true. Now that delving was a safe occupation, there was a better chance some spatial mages decided to try their hand at it...

"Sometimes, there's more to get from a monster than its corpse. This is to help Cluma earn [Proficient Delver], so cost efficiency isn't important."

"True. Good experience for your new class, too. Go ahead then; I don't need anything there for the next hour or so. You don't need me to show you the way."

And he saw through my reasons for asking to borrow his tools instead of asking him to make it himself, too. Well, whatever. He hadn't mentioned any concerns.

"You're not going to supervise?" asked Cluma nervously.

"No, I'm going back to Gordon's office to tweak this engine design before we put the next one together."

"Umm... But... What if Peter blows up your workshop?"

"Then he'll be paying to repair the damage," he replied matter-of-factly, causing Cluma to deflate.

"Don't worry. I know what I'm doing," I said reassuringly, feeling very glad I'd never explained to her the concept of raising flags.

"Fine."

"Why are you building an engine, anyway?" I asked Grover. "What are you going to do with it?"

Vargalas already had electric motors, after all. With lightning crystals, there was no concern about powering them, and they were simpler and easier to build. I couldn't think of any use case where a fuel-based engine of any sort would be better.

"Nothing. We just wanted to see if we could."

A good enough reason, I supposed. If they ever managed it, it would likely get added to the [Engineering] skill, or a higher rank equivalent, so it wasn't as if it would be forgotten about. It would be ready and waiting for someone to find something to power with it.

I made my way to Grover's workshop, where Cluma stood watching like a hawk while I put together my first prototype. Nothing more than a disconnected mana-battery with an inlet but no feeder, inscribed into a bead of steel. No matter what density mana it was left in, it would remain completely inert without someone deliberately pumping mana into it.

I took it outside, tossed it into the air and focused on it with [Expert Mana Control]. My efforts were rewarded with a loud pop as the bead burst apart, but there was no serious explosion involved. Even the shards of the bead hadn't travelled far. As weapons went, the engine was a better one.

... For that matter, if they'd manufacturing ethanol or something equally flammable, couldn't we douse the hydra in that and burn it?

No. Focus. One idea at a time. I'd proven the principle of the thing; an overcharged mana-battery goes boom. Now it was time to scale things up.