Mechanicsburg was full of people who sort of drifted towards them as they walked through it. It wasn't exactly a parade, or a welcome party, just that everyone who possibly could find a reason to be walking their way somehow was. Then the Jägers showed up and that was it for subtlety, because Jägers had never had much use for that to begin with, so they just followed Barry along keeping up a cheerful stream of chatter and...taking bets on how many of the TPU people were still alive? Klaus sort of hoped Barry had missed that.

He hadn't. Barry turned and grabbed the nearest Jäger's arm. "Hang on," he said. "Dimo. You think any of them might not be dead?"

"Vell, it vas makink dem fix it," said Dimo. "Mebbe it decided to keep dem 'til it vas sure hyu vas goink to help."

"It-" Barry stared at him for a moment, then let him go and snarled, "Of course it was." He sped up. "Castle," he barked. "The research party from Transylvania Polygnostic. Do you still have them?"

"Oh, yes." As always the voice sounded weirdly close, as if the Castle could somehow project itself into an invisible presence right by the ear of the person it was addressing. "But now you're here there's no need for contractors."

Barry's head jerked upward, and his voice rang with harmonics that would have prompted the population of many towns to back away slowly, or possibly run full out. "You will release them immediately, alive and unharmed."

"Oh, fine," said the Castle sulkily. "You're no fun at all."

"Thank you." Barry sounded deeply sarcastic. He looked, when he met Klaus's eyes, more subtly relieved and a little haunted. Then he turned away to find the nearest non-Jäger (which took some doing, given their current surroundings) and ask her to see to getting somebody with soup, blankets, and medical supplies to the nearest gate.

The research party was emerging from the gate as they reached it, squinting against the sunlight, their clothing in rags. Barry clapped a hand on the young professor's shoulder and got a start and then a look of total shock.

"Y-you!"

Barry arched an eyebrow. "Me," he agreed. "Don't know what you were thinking, here. I'm expecting enough trouble as it is. Go get some dinner and clean up, all right?"

"They were attempting to discover our secrets while you were gone and I was...less able than usual to protect them. You should have let me squish them a little," said the Castle. "I can still reach from here if you'd let me hit them with a few bricks?"

"No," said Barry. He gestured Klaus in, and the door shut behind them with an unnecessarily theatrical grinding noise and boom. "I'm going to be very nice to them... and I'll consider guilting them about being nosy afterward."

"Hmph," said the Castle, its tone implying it didn't think much of that plan at all. Possibly it just objected to being nice to people on principle.

"So, where are we starting?" Klaus asked.

"Library," said Barry. "The Castle should be able to-"

"Oh dear." The Castle sounded unexpectedly concerned. "I don't recommend that."

Barry paused. "Why not?"

"I-" The Castle's voice dropped, as if it were terribly ashamed. "I can't see it."

"Oh." Barry patted a doorframe absently, then hoisted a death ray and calmly vaporized a giant spiked hammer as it fell toward them. Klaus felt a hot fine film of debris mist down over them. "It's all right. That's part of what we're here to fix."

"Why do we need to get to the library?" Klaus asked.

"Because from there we should be able to figure out where the most serious damage is." Barry glanced at a cracked floor, the other side of it sloping dismally away. "Not necessarily the obvious architectural problems. The Castle's consciousness and control mechanisms."

"The Castle's consciousness is in the library?" Klaus asked. He'd always wondered where, exactly, the Castle's mind was. But the Castle itself tended to be against anyone asking questions, and he suspected Bill and Barry had avoided the subject out of respect for its feelings more than any real disinclination to tell him. He might just be about to find out, though.

Barry paused. "Yes and no. The part we're talking to now, for instance, isn't."

"Right." The part they were talking to couldn't see the library, and was upset about it. Did that make sense? If you cut off the part where its consciousness was, surely it would be able to see the library and nowhere else? But from what Barry had just said it sounded like there might be a different bit that could see the library. Hmm. "More than one centre of consciousness, or the whole thing is one big consciousness?" he asked quietly. Either they had more than one Castle to deal with in different parts or...they had more than one Castle to deal with in different parts, only it had been fragmented by having something blow up inside its brain.

"Normally the latter," Barry said. "You can see why it's having problems. Fortunately," he added, "last time I was in the library, things were working well enough that I think we can get some information there."

Klaus nodded. He'd never imagined feeling sorry for Castle Heterodyne before. "Once we have somewhere to start we should be able to start reconnecting things."

"And once it has full conscious control again - and enough power -" Barry glanced up at the ceiling and then stepped aside, pulling Klaus with him, as a series of stones smashed down. He jumped across a gap in the floor and headed for the next doorway. "Well, after a certain point it'll do the rest of the repairs itself."

"I know trying to kill us is its favourite hobby," said Klaus, dodging as another gap opened beneath his feet. "But you'd think it wouldn't do this to the people who are here to fix it."

"Unfortunately a lot of this is probably reflexive." Barry looked back to make sure Klaus was all right, then glanced upward and added, "Although if any of it isn't, you can cut it out any time now."

"Some of the traps have developed minds of their own," said the Castle, sounding a little sheepish. "Watch out for the fun-sized mobile agony and death dispensers."

"Thanks for the warning," Barry said, sounding slightly rattled. "Do you know where they are?"

"I've lost them," said the Castle.

"Great. I appreciate the warning." Barry shot Klaus a rueful look. "Thanks for coming, I'll try not to get you killed."

"Watch out for yourself as well. Getting killed by Castle Heterodyne would be a much more embarrassing way for you to die than for me," said Klaus.

Barry snorted. "I'll try to avoid it."

"You'd better," the Castle grumbled. "I was hoping for your brother to come back with you, you know."

That got a wince. "Yeah, me too."

Klaus patted Barry's shoulder and left it unsaid that he had too.

Barry shot him a grateful look and forged ahead. At the next doorway, the Castle warned them that they were about to enter a dead zone, where the traps would be entirely uncontrolled. That was, predictably, exciting. The next section of the Castle's divided mind was almost comically surprised to see them.

The library, when they reached it, was much dustier than Klaus remembered, a condition that was not helped when Barry started rolling up the rug. "Hopefully this does still work," Barry said. "A little help here?"

Klaus moved forward, but the Castle apparently took this as addressed to it. "With him here?" it asked.

Barry sat back on his heels. "Yes, with him here," he said testily. "He's come in to help us."

Klaus wasn't sure whether to say anything. He was indeed there to help, but it seemed unlikely the Castle would believe him if it didn't believe Barry.

"You want to be fixed, don't you?" Barry shoved the carpet back on his own, since the Castle wasn't helping, to reveal a complex of colored lights. After some irritable flicking of switches, a skeletal model of Castle Heterodyne took shape, limned in fuzzy green and looking as unfinished as the current interior of Castle Wulfenbach. "Anyway, you like him. Better than you like me, sometimes. So cooperate." He poked at the green framework, and several spots turned a grudging yellow.

Klaus had a moment of thinking they should have brought Doctor Sun, even though his medical expertise was no use on architecture, simply for his vast experience at making uncooperative patients behave. Then he knelt down and looked at the map, following the lines of it with fascination. "Are the fuzzy bits the parts you can't see from here?" he asked the Castle.

"I cannot focus very well at all," the Castle complained. "But yes."

Barry waved a hand through the light at a point Klaus recognised as the library itself, in one of the clearest sections. "It normally looks a lot better than even the best sections of this. But the yellow marks - could you make those red, please? They just look like you're having polarisation trouble - that's better. The red marks are breaks in control and communication." He peered at it for a moment, then gestured to a ball of red fuzz with lines radiating from it like blood poisoning. "That would be where Lucrezia's labs were. Architecturally they're more intact than that looks."

"Work outwards, starting with the nearest red sections?" Klaus asked.

Barry nodded. "We'll want to check back periodically. The map should improve as we go."

The map did improve with their every return to the library, gaining detail, colour, and frequently new and different sets of red highlights. The range through which the Castle and its subsystems refrained from attacking them also improved, although it kept arguing with Barry over whether Klaus should really be allowed to survive knowing this much about it, and then suggesting he should be consigned quietly to life as an experimental subject if Barry was too fond of him to kill.

"I'm not going to kill him," Barry finally snapped at it, "and I'm not going to let you kill him, maim him, trap him, or whatever other sadistic options you happen to think are funny. He is my friend. You are going to listen to me, and you are going to keep him alive and well and safe as long as he's in your range of influence. As diligently as if he were a member of the family, do you understand me? And the same goes for his son."

"Wait, you're telling the Castle? What part of secret didn't you understand?"

"And you won't tell anybody he has one," Barry added promptly. "Including the boy himself. It's Castle Heterodyne, Klaus. It's generally reluctant to tell people things. Anyway, at some point he might want to visit, although I admit at the moment it's hard to see why."

"I'm sure the book has a chapter on keeping your child away from malevolent architecture," Klaus muttered. "And it's careful with your secrets. I'm likely to get blackmailed."

"You've actually talked me into helping you take over Europe," Barry said, blithely and not completely accurately. By this point he sounded much calmer, though his voice still rang oddly off the stone. "I'm not sure there's anything else it could actually think to ask you for."

"How old is the boy?" the Castle put in at this point. "It sounds as if he might have potential as a consort for the Lady Agatha..."

Barry stared at the ceiling. "Agatha is four."

"I am five hundred and eighty," the Castle pointed out. "There is nothing wrong with thinking ahead."

"At least the pressure's off you now it's moved on to the younger generation," suggested Klaus, trying not to laugh.

"He should pay more attention to continuing the line, too," the Castle shot back. "Preferably with someone more cooperative than the last two Heterodynes' wives."

"I will try not to marry anyone who wants to kill me," Barry said, offering Klaus a highly unconvincing mock-glare, then rolled his eyes and rapped on the floor. "Or destroy Europe, although I suppose generally speaking that would be a plus for getting along with you."

Klaus still wasn't impressed with Barry's secret-keeping abilities, and the fact that Castle Heterodyne evidently wasn't either was small consolation. Its apparent conviction that his son would be an ideal match for the Heterodyne girl was simultaneously unsettling and oddly flattering.

He was distracted by the repairs before long. Barry was droning away again, which tended to shut out both ambient noise and in some cases distracting thoughts, and then there was the uneasy interlude in Lucrezia's laboratories. Klaus was sure they could no longer smell of either blood or perfume, but the odor pressed on him anyway, like having a song caught in his head. As for Castle Heterodyne's fears about letting him see its vulnerabilities, in all honesty he was only growing more impressed. Especially by the entire room full of "fun-sized" tiger clanks surrounding one of the last breaks. (To be fair, Klaus agreed that they were likely to be a lot of fun if you were doing the aiming.)

As they made their way back to the library again, the Castle's chatter was growing more peculiar. It reported massive gains in perception and control, but it also reported having discovered new areas occupied by insane fragments of itself. In some cases, they could hear two fragments reporting the same conflict from opposite sides. And some sections kept breaking into music to, supposedly, entertain them while it was busy.

Barry was frowning by the time they got to the library, now with a gleamingly detailed map that flickered alarmingly in large chunks. "That's the last of the control breaks, but you're still having problems," he remarked, after the dying screams of the latest orchestral arrangement.

"Parts of me are resisting reintegration," the Castle agreed.

"Yes." Barry was pacing the edges of the library - not exactly a short walk, and full of random obstacles, as the Heterodynes had obviously considered the library one of many excellent locations to display potentially lethal trophies, artwork, and bric-a-brac. "And they'd probably say the same of you. I think I might have to shut you down."

"I am not broken beyond recovery," said the Castle, sounding rather alarmed.

"Temporarily!" Barry said. "Then enough of a power jolt and I think you should come back up... less internally conflicted."

There was a tense pause. "I am not sure I believe that having shut me down you would willingly return me to a functioning state. You have never liked me."

Barry huffed and brushed a hand through the map again, scattering complicated rainbow-edged shadows across the ceiling. "Mutual," he said drily.

"I will not allow you to shut me down," the Castle told him.

"Don't you have to obey Heterodynes?" Klaus asked it, keeping his voice carefully level.

"Not if the family would be better served otherwise. I have always been the Heterodynes' last and best defence. Allowing myself to be destroyed would not serve the family's interests."

"No, it wouldn't," Barry said evenly. "You're murderous, sadistic, obnoxious, and your likely influence is one of several reasons I want Agatha spending time outside Mechanicsburg. But I have a town and a niece to protect - and I do realise I actually need you." A quiet snort. "Especially since I'm probably going to start annoying people shortly."

"I do approve of your plan to take over Europe," said the Castle. The library doors were trembling slightly, as if it was resisting the urge to slam them. "And your assessment of me is flattering. But I do not wish to be shut down."

Barry rolled his eyes but confined his response to the last part. "I can't imagine it's a comfortable thought, but how long do you think the integration problems will last otherwise?"

"I don't know. Nothing like this has ever happened to me before."

And now Klaus was feeling sorry for it again. The Heterodynes tended towards overengineering their creations to an extent that made them almost indestructible. This was one of their more sensible traits, in Klaus's opinion, but it must be hard for the Castle to find itself vulnerable after five hundred years of nothing getting past its walls.

"I do need you," Barry told it, "but I need you functional. You know that."

"Yes," the Castle agreed. The library doors stopped trembling and remained open, but they looked tense. If doors could look tense. "I am very low on power, though. There may not be enough left for a jolt."

"Okay," Barry said, "that's certainly important to know. I'll check the lightning collectors, but it sounds like something's wrong with your primary power source. So this time you're going to have to tell me where it is."

"Please wait for a moment." Inexplicable music, which suggested that Barry's ancestors had considered captured enemies a type of instrument, played briefly. "You'll have to take a lift down from here." A node on the map lit up. "It is currently in an area possessed by another fragment of myself, but we have communicated and it understands the situation."

"Did it by any chance mention what kind of damage we're looking at?" Barry eyed the map. "That's fairly deep. If we're going to need specialised equipment, I'd like to go ahead and collect it instead of improvising with whatever's lying around in a critical location." Klaus cleared his throat softly, and Barry added as an afterthought, "Or making a second trip."

"You will be fixing a damaged waterwheel. I believe the axle is broken," said the Castle reluctantly.

"This place can't possibly be water powered," said Klaus flatly.

Barry looked thoughtful. "There are some... interesting stories about the Dyne," he said. "And a lingering reluctance to touch it that is adequately but perhaps not completely explained by the possibility that the fish will eat you."

"Yes," said the Castle. "The Dyne is more than water, or it was. At its source it still is. You will see for yourselves soon."

A couple of hours later, they had reset the lightning collectors (so that was what those were) and gone out to collect equipment, plus several of the most curious Jägers for potential assistance with heavy lifting, and now Barry was leaning perilously close to a surging spring of water that was actually glowing blue. It lit the cavern and shone through the stone that curved around it like a broken eggshell. "This explains so much."

"It really does," said Klaus. Like how the Heterodynes had risen to power centuries before the invention of the power sources that gave most Sparks the power to compete with the old warlords.

"The Castle, the Jägers, the ducks..." Barry actually reached down, and Klaus grabbed him by the shoulders and yanked him back before he could dip a hand in the water. Barry looked up at him in bewilderment, the blue reflecting in his eyes and an alarming grin on his face, and shook him off to go back to it. "Stop that."

"If the water here were not the problem, I'd be dumping a bucket of it over you about now," said Klaus. "Ninety percent risk of horrible death?"

Barry paused, still leaning on a piece of eggshell-curved stone, and then - much to Klaus's relief - turned away. "Point taken. Thanks." He waved a hand at the machinery. "This shouldn't be too hard to put back together after all. I can even think of a few improvements. But speaking of the water, something troubles me." He walked downstream of the wheel and out across a bridge dotted with turquoise-luminescent mushrooms, staring down to where the water roiled gleaming around the supports. "I don't believe anybody's reported an uptick in waterfowl with giant teeth over the past few years."

"And even in Mechanicsburg I think that would be noticed." Klaus followed him, trying to find the point where the eerily glowing water became just water. "Is the Castle storing the energy somewhere?"

"Apparently not." Barry gestured at the banks of turtle-shaped energy storage devices. "Not that it knows about, anyway. But in that case, where is it going and how?" He stared hard at the water. "I think there has to be something in the riverbed," he concluded. "But we can't get at it with the water like this. At least it's downstream."

"We'd better get the waterwheel up and running," said Klaus. "Afterwards we might be able to take a look."

"Yes." Barry dragged his attention away from the water again. At least he didn't propose a swim. "Let's get to that. Jorgi, Dimo..."

At Barry's signal, the Jägers he'd invited along practically jumped into the job. The equipment they'd carried down unfolded with only a little adaptation, and after a few hours, considerable incidental hilarity, and only two near-falls into the spring (Barry, much to Klaus's exasperation, and Maxim) the great wheel slotted back into place on its new axle and began turning. A series of blue lights clicked on through the machinery leading from it, and the glow began to dim downstream, as if the wheel's shadow were growing.

"You can be smug about the safety equipment now, if you like," Barry said.

"Maybe later," said Klaus. "Now that the Castle is fully powered we'd better get on with making it some approximation of rational."

"I think I've worked out how," Barry said. "It will be a little fiddly to build, but it's ultimately just transdimensional harmonics."

They took the lift back up to far more brightly lit rooms than they'd left, and Barry began drawing diagrams for his new device and passing them to Klaus, who usually passed them back with suggested changes, annotations, or occasionally incredulous comments scribbled on them. It took a few rounds before Klaus was satisfied it wasn't going to have any deleterious effect on organic brain function. He suspected Barry would have been fine one way or another - and then caught himself up, because however hard it could be to imagine anything really happening to Bill or Barry, he knew damned well it could and had - and he'd sent the Jägers back out again, but Klaus didn't relish having to be revived again any more than the Castle did.

Barry eventually stopped humming and tapped his wrench against the base of what looked, frankly, like a very large lamp. "I think we're ready. Castle, how are your power levels?"

"Decent," said the Castle. "And what will that do, precisely?" It sounded nervous, and was trying to hover a brick out of Barry's line of sight.

"What we talked about," Barry said. "Produce a transharmonic pulse to temporarily knock you out. And by the way, you are not the - actually you probably were the first to try to sneak up and hit me on the head, but the point is, I can tell."

"...I was going to hit your lamp thing if I decided against this," said the Castle, but it dropped the brick.

"It's not a lamp," Barry said. "And that would have been unusually considerate of you."

"Klaus might have turned it on while I was knocking you out," said the Castle.

"Why Castle," Barry said in mock surprise, "you're learning from us." He and Bill had long maintained that in some cases this was in fact an entirely practical reason for taking out the doomsday device rather than the Spark wielding it.

"I've never doubted your intelligence, no matter how deficient I find your loyalty and ambition," the Castle returned.

"Thank you so much." Barry rested a hand on the lamp. Klaus told himself to stop thinking of it that way. "I've actually set this up to trigger the electrical pulse as well afterward, with a minimal delay. You won't be out for long."

There was a long pause during which Klaus feared for both them and the not-a-lamp and then the Castle sighed. "Very well."

Barry pressed his hand down. Klaus felt as if all the sound in the world suddenly just stopped, with a strange heavy inward pressure against his ears and mind. The lights went out.

The pressure stopped.

Barry counted under his breath.

There was a crack of thunder, all the lights blazed up at once, and blue sparks raced across the stones of the floor.

Barry grinned triumphantly. "Feeling better?"

"Yessss," said the Castle, managing to sound ominous despite the innocuous question and the fact that it almost certainly wasn't planning on doing anything. "I believe I am fully repaired."

"Good to hear." Despite the mutual irritation, Barry sounded genuinely relieved. There was a distant grind and boom of stone. "So." He wandered over and rested a hand against the wall. "What do you remember about the attack?"

"There was an explosion...the areas near the explosion were cut off. I could not see...or respond." The Castle was quiet for a moment, then added slowly. "I am sorry for my failure in protecting your nephew."

Barry sighed, tilting his head back and gazing a little blankly at the wall. "I know you would have saved him if you could."

"For a time it seemed the family was gone. I am glad you are not," the Castle replied. Then, more cheerfully, "You will have to bring the young lady here. Even if you wish to raise her elsewhere, she should still be tested."

Barry grimaced. "There's no doubt in my mind that she's Bill's."

"It seems unlikely you would be mistaken, but she cannot be recognised as the Heterodyne without certainty," said the Castle.

"Testing?" Klaus asked in an undertone.

"Blood test," Barry said. "It... tastes... every child of the family. Normally when we're too young to remember, I think." He spread his right hand and tilted it until the light caught the tracery of work-scars, then ran one finger along a very faint one in the web of the thumb. "No serious damage, obviously. I'm not sure Agatha's going to be thrilled about sticking her hand in a giant mechanical mouth, though." Nor, perhaps, was it the sort of behavior one generally wanted to encourage in a child.

"A way to be absolutely certain of bloodline is practical," Klaus mused. "But does your family have to do everything in the most disturbing way possible? What's wrong with a syringe?"

"Lacks style," Barry said, in a tone that was either deadpan sarcasm or the honest product of an aesthetic sense developed... well, here.

"And that would be terrible," Klaus answered, equally deadpan.

"We could skip carpeting the Chapel floor with skulls this time, though, if you don't mind," Barry added, eyes flicking upward.

"I only do that with false Heterodynes," the Castle answered.

"And there are plenty of those already, but do they have to be on the floor?"

"There wasn't any more room on the walls."

"...I can believe that," Barry admitted. Then, "Listen. About the attack." His voice hardened. "It was Lucrezia's doing. As were the attacks on forty-odd other Spark houses around Europe, and the slaver wasps, if you've been hearing any of the news. Bill and I found her." He swallowed. "She's responsible for little Klaus's death, and Bill's, as well as the damage to you. I believe her plan was to copy her own mind into Agatha's and take her over."

The Castle hissed. It was a deeply unnerving sound, and not just because it made Klaus think of gas leaks. "She is dead?"

"Yes." Barry swallowed. "But in case that somehow doesn't stick - in case she already made a copy of herself somehow, that I don't know about - I want you to keep watch for anyone who could be her. And anyone you recognise as having served her. And any Geisterdamen, although I wouldn't really expect them to turn up in town. If you notice any such person, I want them detained, as quietly as possible and without disturbing the tourists. Get Carson to help, and tell me." Grimly, "Don't kill them if you can avoid it. I'll want to question them."

"I shall make sure the torture chambers are prepared," answered the Castle.

"That's not - actually, you know, what the hell. Go ahead."

Klaus gave Barry a look. Not that he really expected his friend to go through with torturing anyone, even Lucrezia. Perhaps especially Lucrezia, when they'd known her as a friend, whatever she was now. "Perhaps we should go somewhere that's less of a bad influence?" he suggested drily.

"I may need to scare somebody," Barry said darkly, then closed his eyes for a moment. When he opened them again, he looked... more like himself. "Not a bad idea, though," he said wryly. "Even if I am going to be living here."

"If you'd care to get ready by the main doors, we do have one last thing to do to celebrate your return," said the Castle, tone gleeful.

"I suppose we do," Barry said, sounding resigned. "Well, Carson's certainly had time to see to warning the tourists." A thoughtful pause. "Not that that necessarily means they left."

"If they decided to stick around to see what the Doom Bell sounds like, that's their lookout," said Klaus. He wasn't looking forward to hearing it himself, but at least he knew what he was in for and could probably avoid actually falling over.

"I wouldn't be overly surprised if Carson charged them for staying," Barry said drily. They both glanced up as the Castle made a sound that might have been a giggle. Or perhaps just a gurgle somewhere in the reconstituted plumbing. "All right, let's go."