“A little extra work that’s terrorizing the welcome house!” Eli says hotly. Squizzle shrieks in agreement. “What’s Mr. Teichman going to say when he finds out?”

Eli: This morning, all the windows were gone. Then I noticed that my compass was pointing in the wrong direction.  Are we suddenly at the South Pole?

Nellie: And to make matters worse, the custodian disappeared — and so did little Ariella!

Squizzle: We had to go find them!

Nellie is a minute away from the welcome house when she spots the polar bear. It lurks behind a mountain of ice, black eyes fixed on Eli’s shoulder where Squizzle is huddled. She elbows Eli and nods silently to the polar bear, and Eli shrugs. What can we do?

Right now, they have a much more dangerous enemy.

The custodian hasn’t noticed them yet. He strides through the ice with confidence. Nellie has no idea how he knows where to go in this endless sea of white — already, she isn’t positive that she can find the way back to the welcome house.

The custodian peers down at a handheld device, then turns sharply. Nellie yanks Eli behind an embankment before the custodian can catch sight of them. “Stay down,” she hisses. “We can’t let him see us.”

The polar bear follows them, taking slow, lumbering steps. His eyes never leave the spot where Squizzle is hiding. Nellie tries to ignore it. She can’t worry about that now.

The ice is endless and terrible. To make matters worse, a wind keeps blowing snow off the icy mounds, into Nellie’s face. She shivers as the cold flakes hit her cheeks and then melt. It’s distracting and slows her down.

She’s used to being the fast one, running ahead and swinging through the trees while Eli follows. The North Pole has made her into someone else, someone who walks sluggishly and complains a lot. It’s all the more reason to catch up to the custodian and find out what he’s up to.

Ahead of them, large mountains of ice rise like barriers. The custodian weaves around the ice like he’s done it a million times. And then, halfway through the mountains, he stops.

Nellie spots it first. “There’s a door!” She has to rub her eyes to see it clearly. At the base of one of the mountains is two rows of ice blocks jutting out from it, stacked into two walls a few feet apart. And there’s a hole in the mountain between the blocks like a doorway, directly into the mountain.

“Wait,” Eli says, his voice low. “If we follow the custodian into there, who knows who else might be waiting inside? There could be a whole army ready to trap us. And it looks like there’s only one way in and out.”