Just as she'd implied, Madame Von Pinn put Agatha down as soon as they were inside, although as Uncle Barry often did, she kept hold of Agatha's hand. Agatha looked around, as much fascinated as she'd been by the parts of the dirigible that looked from a distance like they'd been spun by a really big metal spider. This wasn't like any building she'd been in before, but the most interesting part was that there were other children here. They didn't look like the Geisterdamen's children. The colours and proportions were different, like her, like the other pink and tan and brown children in villages but she'd never seen so many all at once. They'd all paused to look at her, so she lifted her free hand and waved.

"This is Lady Agatha Heterodyne," said Madame Von Pinn.

"I thought Aunt Lucrezia had a boy," blurted a taller, brown-skinned boy with black hair. Agatha looked at him with some astonishment. If her mother was his aunt, she had a cousin.

For some reason, he clapped his hand over his mouth as soon as he'd spoken, and Madame Von Pinn trembled very slightly and very fast, so holding her hand felt almost like holding a bee. "Her second child, Master Theo," Madame Von Pinn said after a few seconds. "Miss Agatha, if you wish to walk or play, you may."

Agatha felt the grip on her hand release and darted up to Theo at once. "You're my cousin," she said. "I didn't know about any before."

"I didn't know about you," he returned, grinning down at her. He seemed friendly. "You're really Bill Heterodyne's daughter?" He looked around, then asked in a hushed voice, even though she was pretty sure Madame Von Pinn could still hear him, "Is he here?"

Agatha shook her head. "Uncle Barry brought me. He says my parents are dead. I didn't really get to know them. My mother left me with servants, but Uncle Barry says they were bad."

"I don't remember mine very well either."

"I think I like having a cousin, though," Agatha decided. She noticed almost everybody else had crowded around, so she turned and smiled at them. People in the villages usually smiled back if she did that, and most of the children here did too. "So who are all of you?"

"Well, I'm Theo DuMedd," said Theo, jumping in, and then told her everyone else's names in turn. They had lots of questions, so many that Agatha almost couldn't ask all of hers, but she still heard quite a lot about their families and their lessons and what Baron Wulfenbach had been doing lately.

"Are you going to be a student here?" asked a boy from the edge of the crowd. His hair was brown and went wildly in all directions, his skin was light with a touch of gold, his clothes were a little too big for him, and he was holding onto a book protectively, like he thought someone might grab it. Theo hastily told her he was Gil Holzfäller, and a nice kid.

"I don't know," she said. "Uncle Barry came here to talk to Klaus. I mean, Baron Wulfenbach."

"Will he make him stop taking things over?" asked one of the oldest students, a serious twelve-year-old.

Agatha blinked. "I don't know that either. He just said they're friends."

Even though Agatha was not convinced anybody else knew more about it than she did, that topic lasted until three of the children Agatha's size started hitting each other, which shocked her, and somebody pinched Gil but she didn't see who. Madame Von Pinn made them stop and told them that it was time for little children to go to bed and take naps.

Agatha wasn't sure about this. She had taken naps, but usually while Uncle Barry was carrying her. And she didn't have a bed, of course. Madame Von Pinn didn't like this, but Agatha assured her that she had slept on the ground lots of times, and spreading out a blanket would be perfectly fine, and anyway the floor felt interesting. This wound up with half the other girls dragging their own bedding down to the floor to find out what she meant. Madame Von Pinn said it wasn't proper and began to pick them back up. Agatha told her it was an important life skill. Three of the other girls fell asleep during the ensuing discussion, and after an alarming crash from where the students older than ten were supposed to be reading about history, Madame Von Pinn decided the children lying peacefully on the floor weren't the ones who needed supervising. She left the doors to the bedrooms open and went away.

Agatha settled down. The floor really did feel interesting. It hummed, not exactly like Uncle Barry did, but still interestingly complicated, almost like music. She could feel it vibrating like when he hummed when he was carrying her. It didn't make her sleepy, though. It made her want to think about things.

She half listened to Madame Von Pinn's lessons for a few minutes, until she saw Gil Holzfäller creep out of the boys' room. Now that was even more interesting than the floor. Agatha got up and tiptoed to the door. She thought about getting her shoes, but Gil was barefoot and she thought about how the grownups' boots rang on the floors here, and padded after him silently.

He didn't go to the door where they'd come in. He went the other way from a classroom and slipped into an opening Agatha had thought was only a bit of shadow. She was impressed. Uncle Barry put secret passages in every building where they stayed more than a few days, and sometimes even into tents, but she hadn't spotted that one. She walked in after him, curious, and stopped in a dark spot while he worked a panel of the floor free and squeezed down into it. He didn't quite close it all the way after him, so it was easy for her to move it again when he was gone. She fit easily through the opening, too, feeling her way in the dark. After a brief close place everything opened up suddenly and she lost her grip on her handhold.

Agatha gasped - the floor was farther away than she expected - but she landed with only a little thump and realized she was in the web-type place again, on a flat piece of metal twice as wide as she was, which would be kind of narrow for Uncle Barry. She peered over the edge, then stood up and brushed down her skirt. There were two ways to go without climbing on anything she couldn't reach. She thought she saw an irregular shape in one direction and walked toward it, happy when she got closer and could see it was a leg, dangling from a metal bar above in the shadows. She patted the foot attached to it and whispered, "Hi!"

The foot twitched, hard, and then pulled up out of her reach. A moment later Gil's face peered down at her from the shadows. He was frowning slightly, more as if she was a puzzle to be solved than as if he was really angry. "What are you doing here?"

"Following you," Agatha said, even though that was pretty obvious from the evidence. She studied the bar he was sitting on, not sure if she could get onto it even if she jumped up to grab it. "I wondered where you were going."

He pulled back and then slid off the bar, landing next to her surprisingly quietly. He was still holding his book. "Just here," he said. He regarded her gravely. "I can show you more interesting places if you promise not to tell the others."

Agatha looked up at him, thinking. He didn't have to show her anything, of course, and she wouldn't know if she hadn't come looking for him, but Uncle Barry had impressed on her that she should ask why when people wanted her to promise things. "I'd like that. But why are they secrets?" she asked. "And if they're secrets why are you going to tell me?"

"I don't want the others to be able to find me when I'm trying to get away from them. But you already know my way out." He clutched his book to his chest, looking faintly disgruntled. "I thought maybe you'd keep that secret too if you promised."

"Oh. I won't tell them," said Agatha. "Whether you show me anything else or not." She liked the other children, but she didn't see any reason to help them find somebody who wanted to get away from them. "But I'd still like to see."

Gil smiled down at her, looking a little shy. "Okay. Thanks." He reached up and carefully balanced his book on the beam he'd been sitting on, then held out his hand. "Are you good at climbing?"

"I like climbing trees," Agatha said, putting her hand in his. "You're gonna be able to reach a lot more things than me, though."

"Yeah." He walked a little way down the piece of metal and then let go of her hand. Below them was another, identical metal walkway. Gil sat down on the edge of it and looked at her. "We have to jump here. I'll go first and catch you, okay?"

This seemed reasonable. "Okay." Agatha watched him carefully, trying to see how he landed so softly. She was sure the physics of it would make sense under analysis. Uncle Barry said most things did if you looked at them right. Then she sat in the same spot and pushed off.

Gil stumbled slightly as he caught her, holding onto her for balance for a moment after setting her on her feet, then let go and held his hand out to her again. The humming was getting louder here, vibrating through the metal they were standing on.

Agatha wiggled her toes against the flooring and grabbed his hand again. "Where are we?" she whispered, then repeated it a little louder because the words got lost in the hum. She brightened. "Ohh. Are those the engines? They'd have to be really big for this thing!"

Gil nodded. "We can see them by climbing down some scaffolding from the end of here. Do you want to try?"

"Yeah!" Agatha started eagerly forward, looking all around. Now that Uncle Barry wasn't carrying her, she could see downward much better, even though everything did fade into shadows and distant globes of light. Gil tugged back on her hand a little as they reached the end of the walkway, and she got down on her knees for a better look at the scaffolding. That wasn't bad at all. Probably more comfortable for grown-ups than the walkway, but the bars were close enough together for her.

Gil went first, with the ease of someone who had done this several times before, pausing to look up at her at intervals. "Is this like climbing trees?" he asked.

"Kind of," said Agatha. "Trees are rougher in texture and less regular." Her hand slid into the angle between two bars and got pinched, and she blinked back tears. "And with less corners."

Gil scrambled back up a few feet. "Are you hurt?"

"Only a little bit." Agatha showed him her hand. The pinch mark was red, but it wasn't too sore when she flexed it.

"Good. We're getting close to the bottom now," Gil said encouragingly.

Agatha nodded and peeked downward. He was right. The corners were annoying, but she told herself triangles were a good structural choice and kept climbing.

The last few meters of scaffolding and the floor beneath it didn't just thrum with the working of the engines; they shook. Agatha stooped down to spread her hands on the floor for a moment, then got up, grinning. "This is great."

Gil took her hand again and pulled her across the shaking floor to a steel door. He carefully tapped at one of the rivets around the edge and then stood on tiptoes to reach the doorhandle. Once he'd pushed it ajar Agatha could catch a glimpse of a room full of pipes and cylinders, with pistons moving rhythmically between them. Gil bent down to say into her ear. "Be really careful, don't touch anything that's moving."

Agatha nodded, peering through the opening. Everything that was moving, was moving very fast. "I'll be careful," she promised, and they edged inside.

It was hot in here, and it smelled a little like the grease Uncle Barry used and a little like woodsmoke and otherwise kind of awful, and it was so loud she almost couldn't think. But it was amazing and interesting and her eyes darted from one mechanism to another, trying to trace how it worked. Gil helpfully pointed out its features and what the parts were called, which required leaning down and nearly yelling in her ear, but Agatha didn't mind. When it got to be too much, she put her hands over her ears, and he nodded and took her back out, carefully pulling the door shut behind them.

Agatha beamed at him. "That was great. Where to next?" She stopped and frowned a little. "Or do you want to read your book now?" He had said he was there to get away from people. Although not her, especially. But she was pretty sure it was too dark to read where he'd been sitting when she found him.

Gil grinned at her. "This is more fun." He looked around and picked a direction. "They're building a lab up this way, there shouldn't be anyone there now. But they leave all their tools behind." He added the last bit with the air of someone sharing a treasure trove.

Agatha brightened and followed him. "I've never been in a real laboratory," she confided. "I'm not supposed to mess with Uncle Barry's tools, either. Usually. He has some for me, but they're not as interesting."

"It's only half a laboratory so far," said Gil. "I haven't managed to get into any of the finished ones."

"I've never seen one being built before either. Just workshops." She looked up at him curiously. "You've explored a lot, haven't you?"

Gil nodded. "It's interesting."

Agatha thought about that for a little bit. "You spend a lot of time trying to get away from the other students?"

Gil looked down at his feet, scowling slightly. 'Yeah. 'Cause I don't have a family or anything."

Agatha frowned. This didn't seem to follow. "Uh, what?"

"It matters," said Gil. "They all like you because your family are famous. And Sparks. The less important your family is the less people like you. And I don't have one."

"Oh." Agatha stopped walking, but she kept his hand. Gil stopped when she pulled back and looked at her. Uncle Barry had said they shouldn't say who they were when they were traveling because bad people were looking for her. He'd mostly meant the Geisterdamen, which was confusing, but he'd explained why eventually, even if it had been when she wanted to go to sleep. When they got to Mechanicsburg he'd said who they were himself. Everybody did seem to be very impressed. "Well... I like you."

Gil smiled at her, face lighting up. "I like you too. I really hope you stay."

Agatha smiled back and squeezed his hand. "I don't know," she said. "Uncle Barry kept us moving almost all the time, but he said we were coming home."

"That would be Mechanicsburg, not here," said Gil. He sighed and then shook himself. "Come on, you might as well see the lab while you are here."

Uncle Barry had been really glad to see Baron Wulfenbach, though. And Madame Von Pinn said she was supposed to take care of Agatha, but she seemed to be staying at the school. Agatha wasn't sure what to think. "If I'm not staying here, maybe I can write you letters?" she said. She didn't know how yet, but she was starting to learn and anyway Uncle Barry would help. "But sure. I bet it'll be a really good lab."

The lab was mostly bare, steel floor and steel walls, with wires poking out of the walls in clumps. There were chains and cranks around some of the walls too, maybe for moving things that were being put into the lab or maybe for moving large experiments when it was done. Tool boxes were sitting by the door, and there were oily footprints around the doorway. Stacks of things they were presumably going to use - more tubes and wires, some gears ordered by size, were on the room's only table.

"They've brought more stuff in," Gil said, running over to examine the gears.

"Ooh." Agatha ran after him, but the table was too high for her to see the top when she was close. She looked up at the edge in exasperation, then spotted a crate and went to try to push it closer. It budged. Slightly. Gil came over to help, and even though he was bigger than her she was surprised by how easily he shoved the crate across to the table.

It put her just about at his height, which was almost comfortable for looking at the table. Agatha crawled onto the table - carefully! - which made room for Gil to stand on the crate instead, so they could both inspect the equipment. Everything had little flying towers on it, like the dirigible. A lot of it had tiny writing, but she was still working on how to sound those things out at full size. "Baron Wulfenbach labels everything, doesn't he?"

"He really does," said Gil. "I guess he doesn't want anything getting lost?"

"There are trilobites all over Mechanicsburg, but I'm not sure they're on all the pieces." Agatha fitted a pair of gears together, thinking. "But I didn't really take anything apart to see."

"I think lots of Sparks put their sign on stuff," said Gil. "Um. Maybe not on all the pieces though. Baron Wulfenbach's really thorough."

"No kidding." She wondered what they were planning to make here. She was pretty sure there were enough pieces to make something, but right now it might be supposed to be part of the lab.

Gil pulled some cogs over himself, then a length of thick wire. He considered it a moment then pulled about an inch of it over the edge of the table and pinged it, getting a rather tinny note. "If we cut some lengths of this I bet we could make a music box," he said.

Agatha wrinkled her nose a little at the sound and then tried not to. It wasn't polite. And it was a neat idea. She tapped two of the gears together with a soft ding, then set one down on the table and tried again. The sound was much duller, more of a clink. "I bet we can make the sound better with the right casing."

Gil jumped off the crate and went to grab one of the tool boxes, heaving it rather awkwardly onto the table before rummaging through it for a wire cutter. "We could try attaching them to another piece of wire, so they can vibrate more?" Gil suggested, uncertainly.

"Hmm..." Agatha stared at one of the walls for a moment, thinking about wires and about the resonant vibration of the walkways, and then started picking through the tools. "I think I have an idea."