Are you sure?” Trenton asked. “What would he be doing out at night?”

“It’s him,” Kallista said. She’d only seen the figure in the shadows, but she knew his walk. “I thought I saw him earlier, when we left the house. I wasn’t sure then, but I’m almost positive.”

Trenton peered into the darkness. “What would he be doing out at this time of night?”

“I’ve searched the city for him for days. And now I see him twice in two hours?” It didn’t make any sense, unless . . . She grabbed Trenton’s arm. “I think he wants us to follow him.”

“Into a dragon tower?” Trenton rolled his eyes. “Sure, we’ll just stroll up to the guard and say, ‘Excuse me, but my friend’s dad went through that door, and we’d like to follow him.’ We aren’t even supposed to be outside.”

“A dragon tower,” Kallista repeated thoughtfully. When she’d been in front of the white dragon, she’d asked her father where he was working, and he’d said . . . What was it? “He said that if I needed him I should go to a dragon tower, that the dragons would know how to find him.”

“Who said that?”

“My father. I think he was trying to tell me something.”

Trenton frowned. “You’ve talked to your father? When? You’ve been looking all over for him since they moved us out of the dorms.”

Kallista swallowed. She hadn’t mentioned what happened with the monarch in the white tower because she didn’t want to tell Trenton what her father had asked her to do, but the time had come to tell the truth—the complete truth.

“What I told you about the bruises before was a lie. I went to the city offices demanding they tell me where my father was. A dragon took me to the white tower. Once I got there, the monarch threw me around and threatened me.”

“Why didn’t you tell me?” Trenton asked.

She dropped her eyes. “My father was there. He asked me to spy on you. But I swear, I wouldn’t. I didn’t.”

She could see the pain of her betrayal on Trenton’s face. “I told the Runt Patrol they could trust you,” he whispered.

“They can,” Kallista said. “You can. I won’t blame you if you don’t come with me tonight, but I have to go. There’s something my father is trying to tell me.”

“What can he tell you that he hasn’t already said?”

Kallista shook her head. “I don’t know any more than I know why he came here tonight. But I have to go after him.”

Trenton folded his arms. “I’m not letting you go alone. But whether you think your father is trying to tell you something or not, I won’t let this jeopardize our plans. He’s not going to stop our plans for the submarine the way he stopped us leaving on our dragons.”

“I won’t let him,” Kallista said. “I swear.”

Trenton didn’t seem completely convinced, but at last he nodded. “All right. How do we get in the tower?”

Kallista looked around. They needed a distraction. Her eyes stopped on the guard’s quad parked only a few feet away from him, and a plan came together in her head. She turned to three of the Runt Patrol kids still standing nearby. “What are your names again?”

“Hallie Meredith,” said a girl with long brown hair and blue eyes.

A tall boy with freckles across his nose said, “I’m Michael. And this is JoeBob.”

“You were the ones who took us to the warehouse to get our dragons?”

JoeBob smirked. “Fat lot of good it did.”

“Maybe I can make it up to you,” she said. “Teasing Ninki Nankas is fun. But how would you like to tease an actual city guard?”

Trenton frowned. “You really think it’s a good idea to get them involved?”

“We need their help,”

“We want to help,” Hallie said. “Guards are the worst.”

Trenton shrugged, and Kallista pulled the three Runt Patrol kids close, giving them specific instructions on what to do and when. She turned to Trenton. “Now we need to find a way to get the guard away from his quad.”

“Let me take care of that,” Trenton said. He took one of the extra smoke bombs out of his pocket and pried open the top. He poured a measure of eucalyptus oil around the inside of the funnel, careful not to wet the material as well.

Kallista squinted her eyes. “Ouch! That’s going to sting.”

“That’s the idea,” Trenton said. He licked his finger and held it up to check which direction the wind was blowing. “This way.”

Keeping a close eye out for any additional guards, they crept upwind of the tower. Trenton used the punk, which had burned almost to the end, to light the smoke bomb. The fuse sizzled, then hissed, turning a bright orange. He tossed the clay ball into the street, waited until a steady stream of smoke was pouring out of the funnel tip, and then shouted, “Fire!”

The guard outside the tower turned and ran toward the cloud billowing up from the street. Pushed by the breeze, the smoke floated into his face a few feet before he reached the bomb. The results were nothing short of spectacular.

As soon as the smoke made contact with the guard’s eyes, he screamed and coughed. He tried to wipe his eyes, but that only made things worse. He tried to back away, but the wind had picked up and the cloud followed him.

One arm covering his face, he turned to run. At that moment, his quad roared to life. “Hey!” he screamed, tears dripping down his face. “You kids get off that!”

“Come get us!” Hallie shouted, waving her hands in the air.

Michael rammed the throttle all the way forward just as JoeBob yelled “Look out!” and pointed to the right. With a clash of gears and metal legs, the quad raced down the middle of the street.

“Come back here!” The guard ran after them, but by the way he was coughing and spitting, Kallista suspected he wouldn’t make it a block before giving up. She hoped the Runt Patrol had a good ride and didn’t crash into anything.

“Let’s go,” she said to Trenton. Sticking close to the buildings, they trotted down to the tower.

“You’re sure you want to do this?” Trenton asked. “I mean, I bet the penalty for breaking into one of these places is pretty severe.”

She nodded. She had to know what was going on. What if her father was in trouble? What if she was the only one who could help him? She tugged at the door, afraid it might be locked, but it swung open without any resistance. They quickly stepped through and pulled it shut behind them.

The tower was lit by flickering gas lamps. A walkway curved along the inside wall. She led the way, and twenty feet or so later, she saw a metal staircase spiraling up through the roof. Unlike the automatic stairs in the white tower, they would have to walk up these one by one.

Trenton had placed his foot on the first step when Kallista held up one hand. She tilted her head to listen for the sound of footsteps clanging against metal stairs. She heard nothing. By now, her father could have reached wherever he was going, but she had a feeling he hadn’t taken the stairs. “Let’s keep going.”

They left the staircase behind and continued to follow the curving walkway. The narrow corridor was thick with the smell of the dragons living overhead. Trenton’s and Kallista’s shadows grew then disappeared as they passed each of the wall-mounted lamps. Almost exactly halfway around the tower, she saw a plain metal door set into the wall. There was a lock on the door, but the door itself was hanging open a few inches, as though the last person to go through had neglected to pull it shut.

Trenton looked at Kallista. “You think he went in there?”

She was sure of it.

Behind the door was another staircase. Unlike the fancy, wrought-iron one going up the center of the tower, this one was plain stone, the steps worn with usage. And instead of going up, they went down. There were no lights on the wall, so when Trenton pulled the door shut behind them, they were plunged into complete darkness.

Reaching out, she found Trenton’s hand, and the two of them followed the staircase around and around. Soon, the air began to feel damp, and the smell of sulfur was replaced by a dank, mossy scent.

Kallista stopped. “Do you hear that?”

They stood silently for a moment, and she heard the sound again. Clank, clank, clank. Like metal banging against stone.

“Come on,” she said, pulling Trenton behind her as she charged down the stairs.

A moment later, her knee buckled as she went to take another step down and instead found smooth floor beneath her. Trenton stumbled over her foot, and the two of them crashed into the far wall.

Kallista shook her head and tried to get back to her feet.

“Look,” Trenton said, and Kallista found there was a faint light filling the area, enough that she could make out Trenton’s silhouette in the darkness. Behind him, a lantern moved down the passage.

For a moment, she almost called out. But what if it wasn’t her father? Or what if it was and he was upset that she had followed him?

Staying far enough back to avoid being seen, they followed the lantern through an array of twisting and turning passages. Several times they noticed staircases disappearing into openings in the stone walls.

At one of the openings, Kallista caught the distinct scent of dragons. “I think these passages connect all the city towers,” she said.

Trenton looked at the narrow staircase. “There’s no way a dragon could fit down that. Unless it was one of the smaller ones.”

“No. But servants could, bringing food and whatever else the dragons might need.”

Up ahead, the lantern went out, and Kallista feared they had lost the trail. Then she realized the hallway widened ahead with lights fixed to the walls again. They crept forward until they could make out a small alcove. Unlike the rest of the tunnels, this hallway was lit by electric bulbs.

Why? What was different about this area?

A figure stood facing a door on the other side of the alcove. As they watched, the man pulled out a pocket watch, glancing briefly at it. The electric lights lit the man’s face, and Kallista set her mouth in a grim line. It was her father. But what was he doing here? And where was he going?

He tapped a metal panel beside the door, and four clear beeps sounded. He pulled the door open and disappeared inside.

“Let’s go,” Trenton said as the door began to swing shut.

“Wait,” Kallista said, staying in the darkness until the door closed with a heavy metal thunk.

Trenton groaned. “How are we supposed to get in now? Those beeps were a code. Now it’s locked.”

Kallista chewed on her thumbnail, thinking. “He led us here on purpose.”

“What are you talking about?” Trenton asked.

“Think about it. What are the chances he would conveniently show up where we were tonight? The unlocked tower, the metal banging sound, the lantern that waited until we saw it?” Had her father followed them from the house? Had he let them see him on purpose?

“This doesn’t make any sense,” Trenton said. “Your father had a chance to help us the night we tried to get our dragons back, and he betrayed us. How can we possibly trust him now?”

“I don’t know,” she said, wishing she had a better answer. “I know I shouldn’t trust him. He’s been lying to us ever since we got to the city. But why? He’s never lied to me in my life. Why start now?”

Trenton pressed his palm against his forehead like he was trying to stop a headache. “You think someone is forcing him to lie? Like blackmailing him or something?”

Kallista nodded. “I don’t know how or why, but I think he’s been trying to give me clues.”

Trenton stared at her, and she hurried on. “The day I saw my father in the white tower, he said a bunch of weird things. Like that he was working in a laboratory. Not a workshop—a laboratory. That’s also when he said the thing about me coming to the dragon towers.”

He studied her eyes. He wanted to believe her, but she’d been keeping so many secrets. They both had.

“You could be leading me into a trap. You and your father could have set this up together.”

She took his hands in hers. “I know you have no reason to believe me, but I’m telling the truth. I swear it.” She thought for a moment. “I swear as a mechanic, and even more, as your friend.”

Trenton nodded. That’s what it came down to, really. They may not have been friends when they first started building Ladon together, but after everything they’d been through, he couldn’t think of anyone he was closer to, anyone he wanted to believe as much. “All right. I trust you.”

Kallista threw her arms around him. “Thank you! I swear I’ll never keep another secret from you again.”

He looked across the alcove. “We should go through the door, right?”

She shook her head. That moment when her father pulled out his pocket watch felt too intentional. A signal? Maybe it was a charade. Maybe there was something he wanted her to know. Something that, for some reason, he couldn’t say out loud. “Let’s wait a minute.”

The beeping sound came from the door again, and Kallista pulled Trenton back. As the door swung open, she glanced down the hallway, trying to remember how far back the nearest staircase was. Would they be able to find it in the dark?

It didn’t matter because her father walked through the door, waited for it to swing shut, then turned down a different hallway without even a glance in their direction.

As soon as he was out of sight, they hurried to the door. Trenton tried the handle. It was locked. He glanced at the metal keypad set into the wall. “Any idea what the code might be?”

If her father wanted her to see what was behind the door, it would be a code she would know. If not, she’d made a huge mistake.

She tried her father’s birthday, her birthday. Simple combinations like 1-2-3-5—the first four prime numbers—and more complex ones like 3-1-4-1—the first four digits of pi. Had he used any other four number combinations in any of the games they’d played?

“Maybe it’s something as easy as 1-2-3-4,” Trenton said. “Or four random numbers.”

She shook her head. “He doesn’t do anything without a reason.” But was there a reason this time? Did he intend for her to discover what he’d been working on? Or was she simply trying to convince herself of something that wasn’t true?

She thought back to the last two times he’d spoken to her. In the white tower and that night in the warehouse. She’d tried to push it out of her mind, but now she closed her eyes and remembered the feel of his hands on her face.

She’d asked him, “Why are you doing this?”

He pulled her close and . . .

Her eyes popped open.

“I know the code.” With shaking fingers, she punched in four numbers: 1-2-2-4. “Please be right. Please be—

The locked clicked. The latch swung open.

He did want her to know. He did. His last words to her had been a clue. The day your mother died, I swore I’d take care of you. Since the day she died, I’ve tried to do what was best for you.

The day she died.

Her mother had died the day before Christmas.

She gripped the handle and looked at Trenton. “Let’s find out what’s inside.”