Mom asked Cassandra to bring the book; she didn’t need to specify which one. On a page in the middle, she stopped and read silently.

“Go on,” said Dad, with a surprising amount of gentleness – eyes never leaving the clock.

“The heart of the opposing Fortress, its source of power and prophecy, is referred to by its dwellers as their Master of Virtue,” Mom said, pausing to look for signs of recognition. “Little is known of this enigmatic stone, but if reasoning can be done by analogy with our own Fortress, their Master – like ours – contains a protocol of great complexity: a mind unto itself, not to be mistaken for a common pebble. In all probability, it does not abide by the laws of pebble magic, but rather serves as the source of them – the beating heart of their Fortress’s pebble network.”

“Wait,” said Orion. “The Master of Virtue is a rock?”

“Don’t interrupt your mother,” said Dad, reflexively. He began to pace the living room, occasionally peeking out the window at the treeline, as if expecting visitors.

Mom went on. “An attack on the Master Stone would be an endeavor as futile as an attack on the Fortress proper. However, there do exist weaknesses in the systems that have been erected around the Master Stone. Our plan of attack hinges on our ability to place Earth into imminent danger of apocalypse, thereby causing the Master Stone to generate prophecies. This technique allows us to force, and therefore to predict, the actions of the opposing Fortress with high probability – including but not limited to their recruitment of specific individuals. We have used this technique repeatedly to place more than a dozen ‘connected twins’ into their ranks (see Appendix H).” Mom stopped reading, tears of awe in her eyes – the way she had gotten at the Grand Canyon that one time. “These words were written by your grandfather more than two hundred years ago. Before the Civil War.”

Mom and Dad waited for them to process. They were pretty good about doing that, actually – one of their better qualities. Orion finally said, “So… Grandpa was like really, really old” – to which they nodded patiently.

The phrase “connected twins” made her think of Styxx – a face on a paper pushed across the school library table (“Have you seen this man?”) The cat version of that face was one that – recent blinks suggested – Aissaba was having trouble getting out of her head.

***

As eyes of various types turned on Aissaba, glittering from beneath hoods in the torchlight, she saw that cat-Styxx was among the crowd – arms crossed and a whiskered smirk on his face. For a moment, she thought he might come to her rescue. Then, she realized that his smirk was that of an entertained spectator, not a savior.

“Do you have one?” said the merchant. Aside from a smear of ash on her cheek, she could have been the woman from the cafeteria. “Hey, I recognize you. You’re one of Master Styxx’s new recruits.”

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Aissaba had been wondering what they called him around here.

“She’s from the other Fortress,” whispered someone in the crowd. “Bet she has loads of pebbles.”

“What’s it worth?” said Aissaba again. On the merchant’s counter, she noticed a book – old and tattered, like the one Joanne Johnson had in her possession. The torchlight gleamed on the gilded words, A Fortress of Pebbles. “How much is that?”

“We have it on a thumbdrive,” muttered Tassadu under his breath. He was right; it would be dumb to trade away a whole pebble when they could just as easily use it to extract the data from the thumbdrive. But Aissaba needed something to break the tension, and the book was calling to her.

The merchant slipped into sales mode like a frog into water. “This copy,” she breathed reverently, “is one of the original copies of the handbook. Printed in the mid-eighteen hundreds and given to operatives on Earth in lieu of pebbles.” She must have seen confusion in Aissaba’s face because she said, “Ah, yes. Being fresh from the other Fortress, you wouldn’t know about our handbook yet, would you?”

Aissaba glanced at cat-Styxx, who still had that arrogant smirk on his face – as if all of this was either going precisely according to plan, or entertainingly better.

“What? It’s like a manual for how to be a Rot Cultist or something?” said Aissaba, eyes on cat-Styxx.

One of his whiskers twitched, with barely contained laughter.

“Yes, and more,” breathed the merchant, picking it up and sniffing the pages as she riffled through. “While one Fortress watches and recruits from Earth, ours watches and recruits from yours. Copies of the handbook contain records dating back to ancient Greece. Essays, observations, fragments, plans – all compiled by the eldest Master of Rot.”

Aissaba thought of a man in a plaid flannel shirt, flipping the bird at the Masters of Language and Mind. She thought of Orion saying, “So… Grandpa was like really, really old.”

“I’ll give it to you for one language pebble,” said the merchant. “And I’ll throw in free food for life at my shop.” She hastened to add of the rotisserie behind her. “It’s not always a grumble pig, mind you. They’re just in season this time of year.”

The smaller of the three cultists ahead of Aissaba in the queue buzzed for several seconds, something Octopus Tentacles translated as, “If you’re willing to talk privately, we can give you an even better deal. We’ve spent the last two years running jobs between Earth and the Master World.” From his tone, he assumed that the opportunist in Aissaba ought to immediately smell something good about this.

“What kind of jobs?” said Aissaba. Cat-Styxx nodded approvingly from the crowd. Suddenly, Aissaba got the feeling that this was some kind of test. One that, like the stairwell and the smokey hydra, she had walked unsuspectingly into. After the last ones, cat-Styxx had given them a suite fancier than anywhere she had ever stayed. What, she wondered, might he give them next?

"You're biting your lip," muttered Tassadu under his breath.