As Vonn lectured about engines, Birb stared at the chalkboard sketches Vonn was doing in preparation for drawing on page after page of a letter. "Okay, how did you come up with that?"

Vonn had been half lecturing, half dictating. He paused, trying not to react to his sister's uneasy expression. "I get the sense that this is so. But we have yet to prove it. I want it to be our knowledge."

Birb tilted her head. "But you're giving it away."

"I want a lot of people using it, developing compatible skills, building parts I can use."

Tazo hummed in thought. "So there's a relationship between pressure and volume and temperature and the amount of gas. Pretty complicated."

"It's the same concept seen in the frostfire engine. He's just coming at it in a different way. I'm trying to get him studying the theory behind it even while he's building stuff."

Birb commented, "If you have this much to say, maybe you should be printing whole essays."

"At some point, yes. Let's wrap this letter up though."

Afterward, he caught Tazo reading the message from the distant Vulin. She flicked one ear playfully and said, "This is what you were fussing about?"

"I hadn't been expecting to hear from, ah, anybody else."

She kept teasing him about that, but reminded him to send another letter separately if he had any sense, not just a pure business message. "And ask if she's got a wizard brother."

#

Polestar came back the next day. He looked exhausted, but pleased. He had a new toy: a shield of glass, round and frosted.

He showed it off at the shop, making it chime when he tapped it. "This was mine, but it got stolen twice. We found it in Baron Kolm's mansion."

Tazo said, "Where'd you afford something like that?"

"It was a... special gift."

"Oh."

Ashfall said, "From who?"

Vonn started to answer non-committally, but Polestar waved him off. "Ash, there's something you might not know about me. The same thing that happened to Vonn and Selen, got me too. We got gifts, not just visions."

The Centaur mare shuffled her hooves and studied him intently. "So you're not just rattled from being a prisoner and a slave; you know things from somewhere else. That other world that Vonn goes on about. And you're claiming the gods themselves gave you something."

"Yeah. I'm sorry to hide that, but I spent around a year not telling anyone because it was so crazy. I got used to hiding. Had no idea I'd ever meet someone like me."

Vonn hung his head, but Tazo put a hand on his shoulder and he leaned toward it. He said, "This is home now. Yours too, if you want."

Polestar nodded, flicking his ears back. Talking about "visions" still wasn't the whole truth, but it was close enough.

Tazo said, "Anyway, has the shield got any unique features? Vonn, did you fill him in about that backpack yet?"

"No. Polestar, this is secret information, but... Selen got a special item too, that turned out to be a hint at something important." He talked about the pebbles of gold magicite in the bag's lining that had an anti-gravity effect. "We'd love to tune a crystal to do the same thing, if we had any idea how."

"Why not have your wizard guy take a look?"

"We didn't show the stuff to him yet. We were worried about getting too much unwanted attention. For good reason." He rubbed his tailtip.

Polestar stamped the floor with one hoof. "Are you trying to make an impact or not? If you trust that expert not to fireball you and steal your discovery, show him what you know."

"It's time, yeah." He tapped the shield with one claw, making it ring. "I've heard of magically hardened glass, but it wasn't on sale in Grandbridge and it hasn't occurred to me to build with it. How strong is the stuff?"

"It takes impacts and falls well. I even stepped on it once by mistake. As far as I know it's not magic beyond whatever was done to make it."

"And there's a handle attached. Not drilled through. I want samples of this glass." He looked around. "May I take a density reading?"

They filled a basin with river water and put the shield in to measure how much the water level rose, to find the volume. Vonn told the story of Archimedes jumping naked out of a bathtub. The workshop had a mediocre scale too. Vonn had Birb work out the weight divided by volume. She declared, "It's lighter than iron."

Tazo said, "There we go, then. Make the next engine from glass."

Vonn answered, "Has to be sturdy enough to... well no, we're not containing explosions in our version. And the critical part is the pressure chamber, which my Well of Energy power helps stabilize. And let's add that topic to the southbound letter, then: can we get this hardened glass or some other light, sturdy material?"

"Aluminum?" asked Polestar.

"It'd be great, but the refining's a pain. Selen hasn't recreated it yet; you need electricity to do it at reasonable cost, not just a tiny zap spell. She does have some kind of material-making power, though."

Tazo said, "Yes, let's look into that, but focus on making this version well. Better-carved parts, better seals."

Vonn nodded. "And a formula we can follow to make more."

He paced, looking around, then smiled and pointed to Ashfall. "Want to give him that gift?"

She fetched a brand-new wind gun from a box in the corner, and presented it to Polestar. "For you! I helped build the air tank, and we finished this up now that iron's starting to come in again. So you already know how to use one of these?"

Polestar blushed. "Thanks! Yeah, I'll learn quickly. Bolt action?"

Vonn answered for her, "Yes. You can borrow my bullet mold for making ammo."

"Thank you both!"