Mellie was the Seed’s premier civil engineer, just like her father was.

Though there was no nepotism involved. True, she'd learned a lot from her parents, which certainly gave her an edge over her peers, but she truly was the most qualified person from the Inside.

Of course, she didn’t directly inherit the mantle from her father, it’d taken her decades to achieve her current level of expertise.

Years of damming rivers, laying out terraced gardens, planning irrigation networks, and managing tunneling operations had allowed her to accumulate the knowledge necessary for her position. Now, she spent her time managing her underling planners, stepping in for the especially challenging problems. Additionally, she is one of the Seed’s consultants.

Something that had always perplexed Mellie was that, for all of the Seed’s geologic shaping prowess, it often made…unsound decisions when it comes to terrain development.

Mellie knew of the Seed’s occasional fallibility, a familiarity that was only reinforced by their frequent interaction.

To Mellie, the Seed was very passionate, though sometimes to a fault.

Like now; it’d taken her away from her duties and assigned her to personally oversee the invasion’s preemptive logistics.

Even overlooking the fact that putting her out here was probably unwise, the whole thing seemed so impulsive.

But perhaps that was merely her age speaking, “Am I going senile?” Mellie wondered to herself.

Lately, she’d struggled to comprehend the urgency with which the Seed so fervently searched out imposters. From what Mellie could tell, it was spooked. The Inside was burgeoning in population beyond the Seed’s means to comfortably support its folk. The solution, as it has been for countless generations of seeds, was to acquire an imposter to be used for the Schism.

Paradoxically, most seedfolk were ignorant of the mechanism that allowed the Schism. Mellie could appreciate its simplicity, at least on paper. The all-important runesmiths would hotly disagree.

The Seed was a unity of two former seedfolk, who alternate between themselves the heavy task of housing the heart of the Inside. When an imposter is obtained by a Seed, the very best mages and runesmiths in the community work to perform the traditional arcana required to build two new housings.

To her knowledge, a housing was a hollow circular ‘cup’ thickly layered in a myriad of unfathomable runes and glyphs. The Seed, and all of its brethren, were comprised of two mentally intimate seedfolk. A housing was surgically implanted into the chests of each one, with the opening of the ‘cup’ facing outwards. The heart of the Inside was then placed inside one of the two housings. Through their combined will and magical skill, the two halves of the Seed work to operate and regulate the runes that help them to control the heart.

They alternate the burden of framing the heart, hence why both have their own housing; it can be passed between each other as necessary.

The purpose of the Seed was to guide the heart to serve the needs of the seedfolk. It does such useful things as enrich the air with ambient mana, pacify wildlife, and exert limited control over the geological layout of its territory.

Mellie had heard rumors of other races who’d discovered how to influence the latter to an extent far surpassing the abilities of any Seed. She wouldn’t be the one to spread these rumors though, the fanatics would be gravely displeased.

Both halves of the Seed must remain close to each other for their mysterious brand of arcane mutual support to function properly. Unfortunately, this further confines it to a small area, which, in the case of Mellie’s Seed, was the brick tower.

The reason for its lack of mobility is not entirely transparent to Mellie, but she’d been led to believe it somehow involved the spatial translation of the heart’s territory relative to the Seed’s heart and the resultant clipping of the territory with solid rock.

For a member of the seedfolk without a mage’s training, her knowledge of the Seed’s nature was a point of pride. It’d arrived to her through various avenues, but primarily via her personal correspondence with it.

Mellie would certainly call herself one of the Seed’s close friends.

Which had her somewhat worried; the Schism could ruin that friendship.

Once an imposter has been obtained and the two new housings built, two worthy seedfolk of opposite genders, for whatever reason, would be selected. They would have housings implanted as it has always been done.

Then, for the first time since uniting, the active Seed’s two halves will be separated…permanently.

Each of these older halves will then go on to unite with their respective oppositely gendered new halves.

Just as everyone else did, Mellie saw the Seed as an individual. In a very real sense, the Schism kills that individual in order to give rise to two progeny seeds. No one wants to experience the death of a friend, especially not Mellie.

But she knew it was necessary, and like many others, she knew it wasn’t really death at all.

Mellie fully understood her selfish reservations for the operation. She didn’t wish to lose a friend and was too old to follow the younger seedfolk on their exodus to a colonial Inside with one of the two newly formed seeds.

And taking this time to ponder over just how selfish her feelings were, was enough to help her quash them. She was the Seed’s premier civil engineer, and she’d do the duty that no one else could perform equally.

Now she understood why the Seed hadn’t pulled any stops and assigned her directly to this mission. Failure is absolutely not an option; all of the Seed’s resources had been invested. Nearly the entirety of the Seed’s able soldiers were here, ready to claim the imposter’s heart. Losing now would be an irrecoverable blow, especially with the siegeanax probing their community’s lands. Besides, the Seed had been acting nervous lately. It was obvious to Mellie that whatever it was, would be a non-trivial factor.

Though loss was impossible, information on the threat posed by infant imposters had been passed down across several generations of seeds and their charges.

But they were well aware that loss might not come at the hands of this imposter, but instead opportunistic enemies. Therefore, it paid to be cautious.

Walking through the flap of her work tent, which was pitched on a rocky outcropping overlooking the maw of the tunnel they were digging, marched one of her favored underlings. This one was especially brilliant; if she had taken on an apprentice during her life, she would have wanted them to be like this inquisitive mind before her.

Without significant formality, as Mellie was never been one for that, he said, “Chief, our Probers have detected the resonant signature of a tunnel being actively excavated by what we assume to be the imposter. It intersects perfectly with the current heading of our bore. Should we proceed?”

Mellie said, “It appears as if it has discovered our presence. Though I have not a clue how; our approach should’ve been undetectable from its perspective.”

As she’d encouraged each of her underlings to do, the relaxed young planner voiced his opinion without hesitation, “Some of the Feeders filling out our army were present when it was discovered. Apparently, it has a handler with telepathic abilities. I suspect that handler has called upon connections amongst its people, which must’ve allowed for it to scout its charge’s surroundings. Perhaps they’ve spied on us?”

Mellie responded, “Perhaps. Have our Probers already drafted a spatial map of their pings? I’d like to visualize the shape of this tunnel for myself.”

“They have, in fact, I have it right here with me,” said the enthusiastic engineer while he handed a capped canvas cylinder to Mellie.

Drawing out the tube’s contents, she studied the rolled-up document. Represented by simple lines in three axes were the tunnels discovered by the Probers. With more detail, physically explored passages had been illustrated.

Probers were a tunneler’s godsend; by tapping at a stone face and listening with the ears they’d been gifted; they could roughly locate tunnels a few hands away. According to the intellectuals of the Varnassi Hegemony, this ability of the seedfolk was not entirely dissimilar to a bat’s sight.

Which made no sense, but they insisted on it.

Frowning deeply, Mellie said, “The number of new tunnels through the stone in this area is staggering when compared to the data obtained by our survey of this region seven years ago. This imposter is, what, eight to ten months old, by the latest estimate? How is this even possible? It’s entirely inconsistent with both imposter behavior and, even stranger, capabilities. An imposter this young should be unable to move so much substrate, even by dumping its tailings on the surface, which I suspect must be the case here. Clearly, we’ve miscalculated.”

Responding to what was likely a rhetorical question, the young engineer said, “Eight to ten months old is right. So, should I go tell the directors to halt the bore?”

“Yes, go tell the third director to pull the active pestle worm out. It’s a shame we’re dealing with an imposter with a sapient handler. I was really hoping we wouldn’t have to deal with traps or other similar shenanigans. In the meantime, I’ll work on the plans specifying how we’ll divert our bore after you leave.”

“Understood chief. I was wondering, should we not simply abandon this excavation now that it knows of our approach? Wasn’t the whole point of boring into its territory to surprise it?”

Without looking up from the spatial map in her hands, Mellie said, “Good question. While that was certainly one of the benefits of this operation, it was by no means the primary goal. The purpose of our tunneling is to bypass the majority of its domain to breach its heartland directly. This way, we will avoid most of its beasts, making the march to its heart all the easier.”

“But won’t it just call the beasts from other regions in its territory to our beachhead?”

“Oh, it would if it could. But it can’t. No imposter can. In fact, even the Seed can’t. Whatever hordes it throws at us will be comprised of only local beasts. I’ve been told that it somehow involves ‘anchor boundaries,’ but I couldn’t really tell you what that means. Anyway, this is why we are excavating a shortcut.”

As he pushed aside the drafting tent’s entrance flap in departure, the young man said back to Mellie, “Thank you. I’ll go deliver your instructions and then I’ll come right back to receive your modifications to the plan!”

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…

My suspicions have been confirmed; as it turns out, the biology of these seedfolk gives them the rudimentary ability to use ultrasonic cave mapping. Through the careful observation of the individuals they refer to as ‘Probers,’ I’ve learned a lot about their workflow.

The Probers impact cleared patches of bare rhyolite with special copper-headed hammers. With their disgusting grimy ears pressed firmly against the surface, they somehow pick up the presence of small cavities anywhere from one meter away, to three. Depending on the geometry.

And I also have a rough idea of their degree of accuracy. I’ve been excavating experimental tunnels of different widths, dimensions, and distance from the natural caverns traversed by these ultrasound cartographers.

Luckily for me, their ability to sense much larger cavities is barely superior to their finer detection. More specifically, they can only detect tunnels wide enough for three humans to comfortably walk side-by-side in when it is separated from them by five meters of coherent rhyolite.

Unfortunately, as they get closer, they can tell if the tunnel in question is flooded with water. I suppose I won’t be preemptively submerging their emergence point. Of course, I can always prepare a sacrificial dam or two somewhere in my dungeon just for them. In fact, I definitely will.