Alek turned back to give her a questioning look.

Deryn jerked her chin back at the storeroom, afraid that if she opened her mouth, the stifled cry of pain would leap out. Alek looked at the glass spheres, then up at the ceiling, and nodded. He steadied the machine, then reached out and turned it off.

The way back was even trickier. Deryn led this time, her foot throbbing, her steps slow and painful across the sleeping bodies. But finally the machine was inside the storeroom again. She and Alek slipped back out into the cargo bay, then locked the door behind them.

As they made their way toward the central stairs, Deryn scanned the sleeping men. None stirred, and a squick of relief competed with the drumbeat of pain in her foot.

But as she climbed the stairs, Bovril shifted on Alek's shoulder and made a soft sound, like whispers in the dark.

Chapter Eleven

"Let me do this," Alek whispered again.

Deryn rolled her eyes. "Don't be daft. I know every squick of this ship. You've neer even been in the laboratory."

"But you can't just sneak into a man's room while he's sleeping," Alek said, his voice breaking from a whisper.

"And you can? You're a barking prince. I hardly think that qualifies you for burglary."

Alek started to sputter something else, but Deryn ignored him, glancing up and down the hallway. After a day that had included a rope-and-winch landing and twenty-eight unexpected new passengers, the exhausted crew was mostly asleep, the airship's corridors empty and dark.

"Just stay out here and keep quiet."

"Mr. Tesla is quite unbalanced," Alek whispered. "Who knows what he'll do if he wakes up? Volger said his walking stick was quite dangerous."

"Aye, there is that," Deryn murmured. Tesla had promised the captain that he wouldn't fire the stick inside the airship. But what if she startled the inventor, and he forgot that he was hanging from a giant bag of hydrogen? "I'll have to make sure I don't wake him, I suppose."

"Why don't we simply tell Dr. Barlow that he's got something in his cabin?" Alek whispered. "The ship's marines can search for it in the morning."

Deryn shook her head. "You know what a sneaky-beak the lady boffin is. She wants it all done quietly, so Tesla won't know she's on to him."

"Of course. The simplest path is completely beyond that woman."

"Listen, if you want to help, wait out here and give the door a wee scratch if anyone's headed this way." She pointed at the beastie. "And keep your eye on Bovril. It'll hear any footsteps before you do."

"Don't worry. I'm not moving from this spot."

"Except to hide if you hear anything." Deryn recalled the whispering sound Bovril had made as they'd left the belowdecks. "If any of Tesla's Russians saw us down there, they might pop up to tell him."

Alek opened his mouth to protest again, but Deryn silenced him with a stern look, pulling Dr. Barlow's keys from her pocket. The largest was labeled LABORATORY, and fit perfectly into the lock.

"Shush," Bovril said with a quiet, anxious rush of breath.

As the door opened, a wedge of the corridor's green light spilled into the room, and Deryn's breath caught. Of course, being discovered right away would be easiest. She was simply a dutiful middy checking on an important passenger.

But Mr. Tesla was asleep in his bunk, his breathing heavy and slow. The moon shone through the window, three quarters full, and the glass instruments that Dr. Busk had left behind glittered with the moon's pearly light.

Deryn stepped inside and leaned back against the door, her heartbeat taking up residence in her bruised foot. The door shut behind her with a soft click, but still Mr. Tesla didn't stir.

A shiny leather suitcase lay open on the floor, revealing a neatly folded white shirt that glowed in the moonlight. The electrical walking stick lay on a laboratory bench, its handle pulled off to reveal a pair of wires. As Deryn's eyes adjusted, she saw they were connected to the airship's power lines. So the bum-rag was recharging his stick, despite his promise to the captain.

Deryn took a few slow steps into the room, her foot still pounding from the contraption landing on it. She knelt by the suitcase and slipped a hand beneath the shirt on top, feeling layer by layer. Nothing but clothing.

She frowned, looking about the room. Dr. Busk had cleared most of his boffin gear away, so the lab wasn't in its usual cluttered state. There wasn't much space to hide anything, at least not anything big enough to create an explosion forty miles across. But the little slivers of lightning had pointed straight at this cabin, so whatever Tesla had found had to be here.

She swore under her breath. It was just like the lady boffin, sending Deryn to search for something without saying what it was.

As she knelt there pondering, a soft scratching sound came from the door. It was Alek, alerting her that someone was coming. . . .

There was nowhere else to hide, so Deryn dropped to her hands and knees and scuttled beneath the bed.

She waited there in the darkness, her heart pounding. There were no sounds from the corridor, nothing except the rush of wind and Mr. Tesla's steady breathing.

Maybe it had been only a crewman walking past. . . .

But then a soft knocking came from the door. Deryn squeezed herself farther under the bed as the sound grew louder. Finally the door opened, spilling wormlight into the room.

Deryn swore silently - she hadn't locked the door behind her.

A pair of fur-lined boots strode to the side of the bed, and she heard Tesla's name amid a stream of whispered Russian. Tesla's voice answered, sleepy and confused at first. Then a pair of bare feet descended before her eyes, and a quiet conversation began in Russian.

Lying there, Deryn realized that something was poking into her back. She reached a hand around and felt an object wrapped in a canvas sack. It was as hard as stone.

Deryn swallowed. This had to be what she was looking for, but it wasn't much bigger than a football. Would Tesla have come six thousand miles to find something so small?

She would make too much noise if she turned over to take a closer look, so she slowed her breath and waited, staring at the fur-lined boots and trying to ignore her own throbbing foot.

Finally the whispered conversation ended. The boots walked away and through the door, and the pair of bare feet shifted as Tesla stood up. Deryn clenched her fists. Was he going to check on his precious cargo beneath the bed?

RA SKULK INTERRUPTED."

But the feet padded over to the door, and Deryn heard the knob jiggle. Tesla was probably wondering how his Russian friend had simply walked in. But after the long and frantic day, could he be certain he'd locked the door before going to bed?

The rasp of a key reached her ears, then the click of a dead bolt sliding closed. The bare feet came back to the bed, which creaked above her as the man climbed back in.

Deryn lay there, listening to his breathing, realizing that she would have to wait for ages to make sure he was asleep again. At least her throbbing foot would help her stay awake.

The mysterious object was still jabbing into her back, and its size still bothered her. How had that contraption detected something so small from the other end of the ship?

Magnetic fields, Klopp had said.

Deryn reached into a pocket and pulled out her compass. She inched it out from beneath the bed until its face caught a squick of moonlight. . . .

Her eyes widened. The needle was pointing straight at the object, toward the bow of the ship. But they were headed south-by-southeast, not due north.

The mysterious object was magnetized. It had to be what Tesla had been looking for.

Deryn counted a thousand slow heartbeats before daring to turn over. She felt the canvas sack in the darkness, and when her fingers slipped inside, they touched a cool metal surface. Not smooth, like cast metal, but as knobbly as a piece of old cheese.

She tried to test the object's weight, but it wouldn't budge from the floor. Solid metal was barking heavy, of course. Even hollow aerial bombs took two men to lift.

What in blazes was this thing?

Dr. Barlow might know, if Deryn could get a sample somehow.

She remembered the chapter from the Manual of Aeronautics on compasses. Iron was the only magnetic element, and a great spinning blob of it at the earth's core was what made compasses work. She rubbed the metal and sniffed her fingers, and caught a tang almost like fresh blood. There was iron in blood, too. . . .

And iron was much softer than steel.

She pulled out her rigging knife and slipped it into the sack. Her fingers searched until she found a wee sliver jutting up from the object's rough surface. Tesla was snoring by now, so Deryn began to saw away at the sliver, the canvas sack muffling the rasp of her knife.

As she worked, her mind spun with questions. Had Tesla's weapon used a projectile of some kind and this was all that was left? Or had the electrical explosion somehow fused all the iron in the frozen Siberian ground?

One thing was certain - Mr. Tesla's claim of having caused all that destruction suddenly seemed more credible.

At last the sliver broke free, and Deryn slipped it into a pocket. She stretched her muscles carefully one by one. It wouldn't do for her legs to cramp as she as sneaking out of the room.

She crawled from beneath the bed and slowly stood, watching the rise and fall of Tesla's chest as she pulled her keys out. The door unlocked with a soft click, and a moment later Deryn was in the corridor.

Alek stood there looking pale, a drawn knife in his hand. Bovril still perched on his shoulder, wide-eyed and tense.

Deryn put her fingers to her lips, then turned and relocked the door. With a beckoning wave of her hand, she led Alek to the middies' mess. He followed, his expression still anxious, his eyes darting down every corridor.

"You can put that away," Deryn said when she'd closed the door to the mess.

Alek stared at his knife a moment, then slipped it back into his boot.

"It was maddening," he said, "standing out there. When that other man stayed so long, I almost burst in to make sure you were all right."

"Good thing you didn't," she said, wondering why Alek was so twitchy tonight. "You'd have started a ruckus for no reason. And look, while I was hiding under the bed from that Russian, I found something!"

She pulled the shard of metal from her pocket and placed it on the mess table. It didn't look like much here in the light, just a shiny black blob the size of Bovril's little finger.

"That can't be what Tesla came here for," Alek said. "It's too small."

"That's just a wee piece of it, Dummkopf. The rest is as big as your daft head."

Alek pulled out a chair and sat at the mess table, looking exhausted. "That still seems awfully small. How did that device detect it?"

"Watch this." She pulled out her compass and set it close to the sliver of metal, which set the needle shivering. "It's magnetized iron!"

Bovril crawled down from Alek's shoulder, getting close enough for a sniff.

"Magnetized," the beastie said.

"I don't understand," Alek said. "What has magnetism to do with an explosion?"

"I reckon that's one for the boffins to ponder."

"I'll ask Klopp as well. We have to know if Tesla's telling the truth before he gets off this ship."

Deryn frowned. "Why's that, exactly?"

Alek drummed his fingers on the table a moment, then shook his head. "I can't tell you."

Deryn's nerves twitched a bit. There was something odd about the way Alek was looking at her, not just exhaustion and nerves. He'd been tense all night, but now there was something stormy in his eyes.

"What do you mean you can't tell me?" she asked. "What's wrong, Alek?"

"I need to ask you a simple question," he said slowly. "Will you listen to every word? And answer me truthfully?"