Now that she knew what she'd been hearing - more or less - or at least where it was, and what sort of being or perhaps phenomenon -

Ahem. Now that Agatha knew something about the Dyne entity, she found she wanted to know more. A part of her sang with it and was satisfied (not a still satisfaction, one rooted-growing-flowing-changing); another part wanted to be able to explain it. And she rather liked it, the way she liked the Castle, knowing it was dangerous and would push her... although the Dyne was not so human as the Castle, and not bound to her.

She spent some time refining the energy extraction and storage mechanism, and sometimes she just visited. She asked it questions and partly understood the answers, and was pretty sure that was mutual. She told it what she was trying to do, what they worried about.

The note was usually gentle with her, but it went pure and piercing when she described the revenants and slaver wasps she'd brought into town for study, throbbing through her whole body. The room twisted around her, Mechanicsburg twisted, and she thought it was the note doing this but it was...communication...a disharmony, a wrongness, no, this should not, can not be, and it was like the pain when the locket had clamped down, but it wasn't what the note was doing to her it was what it was feeling.

...What it was doing to her was undoing, untwisting, unravelling, as if it would tear apart all three dimensions to get at the thing inside its reach, revulsion and inimicality pouring off it, but it felt as if it would destroy her in the process.

'We're trying to cure them!' she shouted at it, forgetting her own earlier efforts not to offend or disharmonise. Anything to break up the sound. 'Ow. And stop that!'

The note shivered, then cooled to a thoughtful soothing hum with a hint of comfort, affection, apology. Reassurance. It is begun.

'Yeah.' Agatha pushed her hair back and found it sticking to her face with sweat. She glared at the spring. 'Excuse me, I think I need a bath now. And not in you.'

Two weeks later she was sitting against the curved rock and trying to make sense of images that might be either the inside of stones or the outside of space when Castle Heterodyne interrupted her musings with the Doom Bell in an alarm clatter. 'My Lady! The wasps have broken containment!'

Agatha was on her feet and running before she registered the triumphant swell of the Dyne note. She stopped, and whispered, 'What have you done?'

And the Dyne sang back, I have freed them.

Agatha burst out onto the wall overlooking the Vespiary Laboratories with a death ray in one hand and a megaphone in the other, breathing hard more from worry than from running. The Castle was prompt, at least. So were the Jägers. A lot of them were inside the compound, fighting alongside the Vespiary Squad.

She forced her breathing to slow, gathered in air, and put all the fury and command she could muster into her voice. 'Wasps! STAND DOWN!'

-And nothing happened.

She stared as a barbed sting went through one of her Jägers, thoughts briefly blank with horror, and then shouted again, louder. Lowered the megaphone and raked the area with her voice alone, in case the mechanical amplification had lost some essential overtone.

Nothing.

If shouting didn't help then more shouting was probably not going to, at least until she figured out what was going on.

Agatha scanned the situation. Revenants were pouring out of their residence halls to join the fight; they weren't doing much damage but they were getting terribly in the way. She tried yelling at them to go back, heard the fraying strain in her voice. They didn't. She'd have clutched her hair if her hands weren't full. The Vespiary had been installed in an industrial area specifically to limit the number of passing visitors, but Mechanicsburgers were nonetheless herding confused and alarmed tourists out of the nearby streets.

A wasp lurched up over the top of the wall at her, and she shot it. More of them were streaming toward her, as if the shouting had alerted them that there was more to the world than the inside of their compound.

Agatha dropped her megaphone and braced her feet as they boosted each other up the wall. She fired downward between reaching claws until she had a heap of scorched carapaces beneath her and jumped. They rolled and crunched under her feet and deposited her in a puddle of green slime. She got her feet under her, twisted the dial to a precision setting and charged into the fray.

The Jägers were still having fun, despite injuries that horrified her, she'd have to fix that later if she could, and some of them whooped when they saw their Heterodyne come to join them. Her grim mood was catching, though, and they closed around her watchfully as she made for the front, firing through heads and thoraxes.

She got out in front where she could fire with a wider beam, but that put the wasps in her face, leaping up as fast as they fell, cool barbed claws brushing her skin and hot blood trickling in their wake. She snarled and her gun cracked, limning them in angry green crackles before they went down, and she threw herself against them. Had to get to the laboratory.

She hadn't seen the swarm yet. She had to reach the hive queen. She remembered the grip of hard serrated legs on her arms, knifelike tarsal claws prying her lips apart... Remembered Passholdt and its cannibalistic revenants, remembered Rovainen, remembered watching the slaver whine above her, she would not let this happen to her town.

Something grabbed her by the hair, yanked hard, and seized the back of her collar when she staggered. Agatha was trying to twist around for a shot when she saw green hair and recognised that those were human knuckles digging into the nape of her neck. 'Zeetha,' she gasped.

'They're getting over the wall,' Zeetha snapped, and the rage of battle washed away in a sick flood of icewater. 'Get out of here, and tell the Castle what to do!'

Fifteen minutes later, Agatha was sitting on the wall beside Zeetha, supervising as the Castle mopped up the wasps, the Jägers collected the wounded, the Vespiary Squad carted live caged samples into the laboratories and the researchers soothingly herded the revenants back indoors.

She said, 'I've got to learn to watch that, don't I?'

Zeetha elbowed her sharply enough Agatha expected a bruise. 'Stealing my lines again, zumil.' More seriously, 'You really do. I know you like to get hands on, whether it's Spark-work or running into danger.'

'I don't like-'

Zeetha batted away the protest. 'Fine, you don't like it, but you still do it. Because you feel responsible. I'm not saying it's a bad impulse. But the town needs you, and some of the people - and the Castle - will listen to you in ways they won't listen to anybody else. You're a war queen. Act like one. Sometimes that means remembering you're responsible for more than what you can do with your own two hands.'

Agatha sighed. 'Right. I didn't think about that.'

Unexpectedly Zeetha grinned at her. 'You haven't had to until recently. I got it drummed into me since I was tiny, probably because it's something both my parents had a terrible time learning.'

Agatha was surprised into a laugh. 'Well, one of your parents is going to want to know what happened to his research installation. So I guess my first responsibility after I take care of the Jägers is to figure that out.'

-freed them-

The town and the Castle listened to her. The wasps and revenants hadn't.

Once she figured out what was going on, she was either going to yell at the Dyne or thank it.

Weeks after seeing Agatha installed in Mechanicsburg, Klaus hadn't been back yet. They weren't out of touch - the wasp-eaters were also more or less safely ensconced there, along with most of the revenants they had identified, and both Dr. Bren and Agatha sent him regular reports. Well, Dr. Bren sent reports. Agatha sent surprisingly chatty and sometimes more informative updates. He'd meant to look in on the progress in person.

But it felt as if a full quarter of the Empire had, entirely predictably, leapt on the new precedent and demanded to secede, and as ever he'd been busy. It helped that most of the towns wanting out did not in fact fit the same parameters as Mechanicsburg, which - as Agatha had insisted - never had attacked the Empire. (She'd had the sense not to say it hadn't attacked Wulfenbach lands.) Too, he'd absorbed Mechanicsburg still hoping that Bill and Barry would come and take it back one day, so there had been all sorts of provisions for turning it back over. Still, there was more to squelching them than simply saying no.

Klaus picked up yet another envelope with a sigh and flipped it over, only to see a trilobite seal when he hadn't expected anything from Mechanicsburg for another week. 'What has Bren done now?' he asked it aloud. The last off-schedule letter from Agatha had informed him with some agitation that Dr. Bren inexplicably thought he needed a mobile hive queen. Klaus had hastily told both of them otherwise in no uncertain terms and felt his hair trying to stand up for the rest of the day.

Klaus flattened out the note. The handwriting on this one was calmer, at least.

Herr Baron,

We may have a cure for revenants.

The revenants you sent here no longer provoke any response from the wasp-eaters, nor do the wasps. They also no longer respond to my voice, and the physiology and behaviour of the wasps have changed. Actually, the wasps tried to escape, and we had to kill most of them. We have preserved a few live and dead specimens for inspection, but if you want to see them, please come at the first opportunity.

I have a possible explanation but would prefer to discuss it in person.

Agatha

This was entirely too interesting to delay for the ceremony of a formal visit. Klaus annoyed Boris by unilaterally rescheduling several appointments and simply took a small airship down to Mechanicsburg himself, startling several of both his own and Agatha's guards when he emerged. He got directions to Agatha, who was climbing around some small scaffolding and twisted around to wave when he called out. Klaus went over for more convenient conversation - and to see what she was working on that required a scaffold. 'Ah! You've found the chariot.'

'It wasn't exactly hidden. Did the Heterodyne Boys actually use this or are people pulling my leg?' Agatha asked, perching sideways on the back of the nearest mechanical horse.

Klaus glanced up, amused partly by the question and partly that she was asking him as a more reliable source than Mechanicsburg. To be fair, Castle Heterodyne, at least, probably would try to tell her Bill and Barry had done any number of bizarre things to see if she'd try to emulate them. 'Yes. They made an effort to avoid disturbing people, but sometimes it was very obvious their sense of aesthetics developed here.' He patted the horse's nose, then jerked his hand back before the ensuing lunge and snap could take it off.

'Hey!' Agatha smacked the glossy black-metal neck, producing a resonant bong. 'No biting friends.' She shot Klaus a slightly embarrassed look. 'Or allies.'

'It always does that.'

'Well, it can stop.'

'I got your letter,' he said. 'You said you had some idea what was going on?' It was certainly more than he had.

'Yeessss.' Her hesitation seemed less uncertainty than contemplation. She patted the horse absently. 'How much have you ever listened to Dr. Yglyn?'

Klaus raised his eyebrows. 'This has to do with a threat to the three-dimensional world?' he asked skeptically. The fact that Mechanicsburg had a shoggoth made it slightly more plausible than otherwise, but he was pretty sure Dr Yglyn was making most of it up.

Agatha snickered. 'Well, not more than usual.' She went serious, then, and a little distant, as if her mind were somewhere else. She hummed a few notes that were not quite heterodyning and made the back of Klaus's neck prickle. 'There is an extradimensional... entity, though.'

'I take it you're not warding it off with ceremonies and donations of hair?' said Klaus. 'What is it doing?'

She looked levelly at him. 'Powering Castle Heterodyne.'

Klaus stared at her for a moment. 'Are you telling me the Heterodynes captured an extradimensional entity to power their Castle?'

'Not captured! Built on top of. It -' Agatha waved her hands in a way that was alarmingly reminiscent of Dr. Yglyn. 'Communication is... interesting. But having its energy consumed seems to be beneficial or satisfying for it. I think it regards us as a way to extend its influence.'

'Have you been consuming its energy?' He kept his voice level despite the jolt of alarm.

'Only a little,' she said. 'The Castle seemed worried about it.'

'Even Castle Heterodyne has that much sense,' snapped Klaus. 'You discover a creature from another dimension in your basement and start letting it feed you energy? You seemed more grounded than that.'

Agatha waved a hand. 'A very little. I'm all right, honestly. But the point of all this is, it has a violent distaste for mind control.'

Klaus paused, distracted from snapping at her again. That information made consuming energy from it more of a gamble than outright madness. 'You think it's curing revenants?'

'Yes! Almost definitely. Everything fits. Nearly everything,' she added with a sudden frown. 'Fraulein Snaug has recovered, but I'm not sure why she hadn't before.' Klaus couldn't begin to guess yet, although at least Snaug's misfortune had allowed them to determine that revenants didn't automatically do the most alarming thing possible in response to Agatha's normal tones.

He held out a hand to her, avoiding the horse's head as it made to snap at him again. 'Show me?' Either the cured revenants or the cosmic entity itself, but something he could see for himself.

Agatha took his hand and jumped down. 'Of course.'

They started with the wasp-eater laboratories. The weasel constructs seemed to be thriving but showed no more interest in a confined wasp than in a plate of dead hornets. When taken to the revenant quarantine - soundproofed living quarters whose inhabitants still seemed uneasy but more hopeful than last time he'd seen them; Agatha considerately didn't enter - they showed no interest in the people there either.

'We'll want to check with the wasp-eaters that haven't been here, of course,' Agatha said, when Klaus rejoined her to return the wasp-eaters to the laboratories and wander around looking at notebooks and specimens. 'And revenants who haven't been here, if you've found some more.'

'Some, yes. We can check that it's not the wasp-eaters who have been altered by introducing them.' Some of the captured wasps, Klaus noted, were a new type, a little smaller than the ones he'd seen before and with forelimbs ridged rather than bladed. 'You said the wasps themselves had been changed? Is the entity altering them to no longer use mind control?'

'I think it's reversing changes Lucrezia made to them,' Agatha said. 'It claims to have freed them, although I could wish that had been a little less dramatic. The soldiers look mostly the same as before. That, as far as we can tell, is one of the slaver caste.'

'Certainly no one's in danger of swallowing one,' said Klaus, feeling rather stunned. It certainly wasn't an unwelcome development. It was just hard to believe. 'You said you had to kill most of them?'

'Once Lucrezia's alterations expired, they did try to take over the town by more, ah, conventional means,' said Agatha. She ran a hand back through her hair, looking embarrassed.

'Was there much damage? Casualties?' Klaus probed. It shouldn't have been too bad; there were reasons Mechanicsburg was a good site for this type of research. But she seemed troubled.

'No deaths. A lot of injuries. Of course they broke things on their way out of containment, but none of the research notes were lost.' She smiled ruefully again, and he noticed there had been cuts on her face, healed nearly to invisibility. 'Ultimately, a lot of well-fed Jägers.'

'I didn't send you the specimens to feed to Jägers,' he said. 'But I'm glad to hear it was no worse. I'll examine the detailed reports later. Even with giant slavers-' He gave the nearest one another mildly incredulous look. 'Bren's containment should have been adequate to the task.'

They left the laboratory, Klaus still trying to absorb the hope that being a revenant really wasn't permanent and the frustration that the cure might have been in Mechanicsburg all along. 'Well,' said Agatha, 'do you want me to try to introduce you?'

'Yes.' Despite any misgivings he might have about relying on a cosmic horror he was eager to see it for himself.

'I am not entirely sure whether it will be able to communicate with you, but it'll probably be worth the visit anyway.' She smiled wryly at him. 'I argued with the Castle about it the whole time you were visiting the quarantine.'

'I appreciate the effort,' he said, smiling back. 'If being here is a cure then we'll have to use it - but I'd like to see what I'm sending people to be affected by.'

'I don't blame you. It's amazing, but I'm not sure there's anything I can tell you that's reassuring.'

'I still think it's a bad idea,' the Castle said rather sulkily.

'What's he going to do?' Agatha asked it. 'Try to take it home with him?'

The Castle grumbled a little more, but it didn't actually try to stop them. Klaus watched Agatha as she led him in and down. She'd been happy in Mechanicsburg the last time he saw her, exhilarated by its welcome, though not untroubled by its darker side - but still not familiar with it, and still a little stunned by its being hers. Now she seemed to have grown into it.

His attempts to analyse Agatha herself flew out of his head when she laid a hand on an enormous pair of double doors and they burst open with a flourish on a room - a cavern - that made them look small. His eyes passed over the turtle-styled energy storage and an assortment of other complex machinery to fasten on something he could only describe as a river boiling up out of an egg.

'The Dyne,' he said, remembering old stories about it as he stared at the crackling blue energy. 'It lives in the river?'

'Yes.' Agatha beckoned him toward the spring. Being a Spark and therefore possessed of a greater degree of curiosity than most people deemed healthy, he went. She started heterodyning, eyes falling shut, and then her voice... skipped oddly, and struck and held a single note that had to be partly extradimensional because no ordinary sound frequency had ever sounded like that.

It didn't bring up the memories the Doom Bell did, but it evoked all the physical symptoms of intense anxiety and made his jaw ache. Klaus clenched a fist and counted, fighting not to simply break in and tell her to stop.

She did. Not more than seven seconds. 'I brought a friend,' she said, looking between the arching stone shards at the water, then glanced up at Klaus. 'Ah, are you all right?'

He blinked, trying to fight the feeling that the cavern was not quite right, not quite real, hiding something terrible behind it. 'I take it that doesn't have an effect on you?'

'It does, but it hasn't been a distressing one since I figured out what was going on.' Her voice was quiet and concerned and there were Sparky harmonics in it that reminded him of Bill rather than anything more unearthly. 'Before that I spent a while with everything seeming... off, wrong, out of place.'

'Yes.' He didn't quite manage not to shudder, slightly. 'Does it fade, or is it because you have a connection?'

'In my case I think it was establishing or... recognising the connection. But I haven't exactly been dragging a lot of people down here to hum at them.' Agatha drew her eyebrows together and then put a hand on his arm. It was unexpectedly steadying: the sense that there was something about the cavern just beyond seeing didn't fade, nor did the peculiar geometry of the mechanisms, but he was able to view them both as a part of the universe that was difficult to understand but not intrinsically appalling. 'I have not been feeding the springwater to anybody, either, by the way. The effect on the revenants and the wasps seems to be down to the residual influence in the regular drinking water.'

'And the drinking water is safe, or Mechanicsburg would have started digging wells elsewhere.' They could bottle it; the Dyne was a river, they could take barrels of it.

'Evidently there were wells in use before the Castle started using up the energy. After that the river water seems to have been fine, or at least, not to have any effects obvious enough to keep people away.' Agatha made a gesture of exasperation. 'The only false note here is Snaug remaining a revenant in the Castle itself for years.' The spring splashed, somehow sounding irritated.

'Not actually a counterexample,' said Klaus. 'No one had much confidence in the Castle's plumbing. Food and water were delivered, not always from local sources, but the main water supply for the prisoners was rainwater out of the cisterns.'

'Ah!' Agatha tilted her head and hummed briefly again. His skin didn't crawl as much this time. 'I think it likes the idea. Of having more people drink, I mean. The secrecy may be more a Heterodyne thing than the entity's.'

'Are there going to be side effects?' Klaus asked. 'If it's that eager, will it bring people under its control?'

Agatha made a face and shook her head as if a fly had buzzed past her ear. 'It is rather emphatic about not controlling people, but it does... change, does influence. When it was just a spring and a pool, people used to wash in it when they were desperate enough for healing to risk having it kill them. It's been modifying Heterodynes ever since the first one was crazy enough to drink from it. The Jägerdraught is, I am not kidding, an elaborate effort to make it safer.'

'Safer,' Klaus said. 'I am somehow more surprised that your ancestors tried to make something safer than that they decided to drink from something with worse than a ninety percent death rate.'

Agatha snorted. 'I'm not sure they consulted anybody about the statistics first.' She caught her lip between her teeth and pushed her hair back with her free hand. 'I realise none of this sounds very reassuring, but on the other hand... I'm not aware of any problems attributable to it downstream - for, you know, the past few centuries. And it seems very fond of the people who drink from it. It's happy about the old Heterodynes going out and changing things but it's just as proud of Bill and Barry.'

'So, very much like Mechanicsburg as a whole.' An actual giggle escaped her, and he was able to look at Agatha directly instead of the eye-pulling glow. 'Not that I normally expect rivers to have any moral opinions at all. But the point is well made regarding the downstream flow. I'll have to investigate the prevalence of revenants between here and the Danube.' He frowned. 'And any other signs of strange behaviour.' Although he wasn't sure what he was looking for.

'Behaving like Mechanicsburgers?' Agatha suggested.

'...I'm not sure whether I'd want that to spread, certainly,' said Klaus, not entirely seriously. Although Mechanicsburg's level of scary devotion was perhaps best limited to one town.

'Let me know what you find.' Agatha was the one caught gazing at the light, now. 'And if you want to continue looking for another cure here, we can change the water supply. But the sooner we can do something for the revenants...' She looked up at him, green eyes a little haunted, and not by the ghosts of blue light. 'They can talk more freely now. About what it was like.'

Klaus swallowed. He should talk to them himself, find out. But it couldn't possibly be anything good. 'I don't want to start handing out Dyne water to all of Europa as inoculation when I don't know what it's doing,' he said. 'But known revenants, the ones we've already found...I'm not sure it could be worse.'

Her shoulders relaxed. 'Good. I'd hate to-' After a moment she resumed, 'It makes sense to be careful. We don't even know yet how much is required for the cure - although we can get an estimate on that - or even if there's a threshold preventive effect short of the Jäger transformation.'

River or not, desirable or not, they literally couldn't get all of Europa's drinking water from the Dyne. 'We may have to get volunteers to test that.'

Agatha recoiled, making a face as if she'd bitten into a green persimmon, then took a breath and nodded. 'Now that there's a cure.'