“Hi! You’re back!” said Annie.

The narwhal was about ten feet away. He was swimming near a sheet of ice that jutted out from the shore. His ivory tusk was pointed at them.

“Is something wrong with him?” said Jack. “Why is he here?”

“He wants to tell us something,” said Annie.

“How do you know?” said Jack.

“I just know,” said Annie. “I’m going out to him. I’ll crawl on the ice.”

“No, don’t!” said Jack. “It could crack.”

“Don’t worry, it’s really thick,” said Annie. “It’s probably been here for thousands of years.”

Annie stepped out onto the packed ice. Then she got on her hands and knees and began crawling toward the narwhal.

“Careful!” said Jack.

“I got it,” said Annie, reaching the edge of the ice.

The narwhal raised his head above the water.

“Hi, you! What’s up?” said Annie, grinning. “Why did you come back?”

The narwhal made noises that sounded like a door creaking. Then he tapped Annie’s head with his unicorn horn.

Annie laughed. “Thank you!” she said.

The narwhal then turned and swam away. He soon disappeared under the water.

Annie crawled back toward Jack. She stepped off the ice sheet onto the shore.

“That was so cool,” she said.

“What happened?” said Jack.

“Simple,” said Annie. “He came back to thank us.”

“You’re kidding,” said Jack.

“Nope,” said Annie. “That’s basically what he said: Thanks. And then I said thanks back.”

“That’s all?” said Jack.

“That’s enough,” said Annie.

Jack took a deep breath. “Okay! Now we can leave!”

He and Annie quickly walked over the slope. The tree house was still sitting on the pebbly shore. It was lit by the orange and red light of the Midnight Sun. Jack and Annie slipped through the window.

Annie grabbed the Pennsylvania book that always took them home. She pointed to a photo of the Frog Creek woods. “I wish we could go there!”

Nothing happened. The wind did not start to blow.

“I wish we could go there!” Annie said again.

The wind still did not start to blow.

“Why aren’t we leaving?” said Jack.

“Let’s look at our rhyme,” said Annie, “at the last verse.”

Jack pulled the rhyme out of his bag. He read aloud:

Explore different worlds.

Show friends where to go.

“Okay! We did that!” said Annie. “We showed our friends where to go—we gave Leif our map! And we showed the narwhal how to escape from the shallow water!”

“Yeah, we did all that,” said Jack. “And I wasn’t even thinking about the rhyme!”

“Read the rest,” said Annie.

Jack read the last two lines:

Unite all these worlds

With a word that will glow.

“I forgot about those lines, too,” said Jack. “What do they mean? What’s the word?”

“I don’t know. But if it glows, it must be written down somewhere,” said Annie. “Check your notebook.”

Jack pulled out his notebook, and he and Annie looked at it together.

“Oh, man. I forgot to take any notes,” said Jack. “What about our Greenland book?” He took out the Greenland book and thumbed through it. “Nothing glowing here.”

“Wait, what about our message to Leif’s family?” said Annie.

Jack reached into his pocket and pulled out the crumpled note. He and Annie looked at it together.

“Nothing,” said Jack.

“Hold on!” said Annie. “Look at the letter T!”

Annie pointed at the letter T near the bottom of their note. The letter seemed a little brighter than the other letters. Then suddenly it glowed like it was on fire. Next to the T, the letter H grew brighter. Then A grew brighter. Then the next letter, N.

One by one, the letters grew brighter—until T-H-A-N-K-S was all aglow.

“Thanks!” cried Annie. “That’s the word!”

“Thanks?” said Jack. “Why thanks?”

“I’ll explain when we get back,” said Annie. “We can go now.”

Annie pointed at the picture of Frog Creek again. “I wish we could go there!”

The wind started to blow.

“Yay! It worked!” said Jack.

The tree house started to spin.

It spun faster and faster.

Then everything was still.

Absolutely still.