When Mom and Dad came back, Hugo told them he was going out to the big windows to get some fresh air. But instead, he made his way down to the lower deck. He followed the route that they’d taken with Mr. Singer earlier.

He was going to sneak into the cargo area and get Panya.

The hallways were quiet, but Hugo heard voices whispering from some of the rooms. Twice he had to duck behind corners to avoid being spotted by members of the crew. But luckily there was no guard posted in front of the door leading out of the passenger area. He managed to slip through without getting caught.

The inside of the airship’s body was very dark, and it took a moment for Hugo’s eyes to adjust. Earlier, the light of the sun had shone through the Hindenburg’s skin, giving the interior a bright glow. But now the air looked inky black. The few bulbs hanging from the girders cast a ghostly light.

Hugo swallowed hard and headed down the narrow walkway until the noises of the engines pounded in his ears. He kept walking toward the very back of the zeppelin. He passed a very big sign with the angry-looking words:

ZUTRITT VERBOTEN

Hugo was pretty sure that meant something like keep out.

He was in the cargo area now, surrounded by shelves piled high with trunks and crates. Above him, the gas bags whispered quietly.

And then a familiar sound:

“Garoo, garoo, garoo!”

Panya must have smelled Hugo coming, and now Hugo just had to follow the howls. He walked to the very back, and there was a big wicker cage. Hugo popped open the door and Panya leaped into his arms.

The little dog’s tail whipped back and forth. Hugo stood there for a moment, nuzzling his dog, happily accepting a shower of slobbering licks.

“Gertie needs you,” Hugo whispered. “And now you have to stay very quiet.”

Panya looked at Hugo, his eyes suddenly alert.

Let’s go, he seemed to say.

But before they’d even made it out of the cargo area, Hugo heard footsteps.

Someone was coming!

He ducked behind a large wooden crate, tucking Panya into his shirt.

“Shhh,” he warned.

Peeking up, Hugo could see the shadowy shape of a man heading toward them.

Hugo figured it was a member of the crew on a nightly inspection.

But as the man got closer, Hugo could see a fuzzy puff of hair and the glint of round glasses.

It was Mr. Singer!

Hugo almost jumped up. Mr. Singer must be looking for Hugo. He wanted to help him find Panya!

But wait.

Hugo had told nobody about his plan to sneak back here. So how would Mr. Singer have known to come looking?

And if he wasn’t coming to help Hugo, what was Mr. Singer doing in this forbidden area of the zeppelin? He’d said himself that not even he was allowed in this rear cargo area.

The hairs on Hugo’s arms prickled as he watched Mr. Singer study the shelves. Finally, Mr. Singer stopped at a large wooden box. He lifted the lid and rummaged inside. Moments later, he pulled out a large envelope.

In the low light, Hugo could just make out a huge swastika stamped onto the front.

And words in big block letters.

STRENG GEHEIM!

Again, even without knowing German, Hugo understood. Whatever was inside that envelope was important.

Hugo’s whole body tingled as it suddenly dawned on him.

Marty’s father was the spy.