“Help! A monster!” said Annie.

“Yeah, sure,” said Jack. “A real monster in Frog Creek, Pennsylvania.”

“Run, Jack!” said Annie. She ran up the road.

Oh, brother.

This is what he got for spending time with his seven-year-old sister.

Annie loved pretend stuff. But Jack was eight and a half. He liked real things.

“Watch out, Jack! The monster’s coming! Race you!”

“No, thanks,” said Jack.

Annie raced alone into the woods.

Jack looked at the sky. The sun was about to set.

“Come on, Annie! It’s time to go home!”

But Annie had disappeared.

Jack waited.

No Annie.

“Annie!” he shouted again.

“Jack! Jack! Come here!”

Jack groaned. “This better be good,” he said.

Jack left the road and headed into the woods. The trees were lit with a golden late-afternoon light.

“Come here!” called Annie.

There she was. Standing under a tall oak tree. “Look,” she said. She was pointing at a rope ladder.

The longest rope ladder Jack had ever seen.

“Wow,” he whispered.

The ladder went all the way up to the top of the tree.

There—at the top—was a tree house. It was tucked between two branches.

“That must be the highest tree house in the world,” said Annie.

“Who built it?” asked Jack. “I’ve never seen it before.”

“I don’t know. But I’m going up,” said Annie.

“No. We don’t know who it belongs to,” said Jack.

“Just for a teeny minute,” said Annie. She started up the ladder.

“Annie, come back!”

She kept climbing.

Jack sighed. “Annie, it’s almost dark. We have to go home.”

Annie disappeared inside the tree house.

“An-nie!”

Jack waited a moment. He was about to call again when Annie poked her head out of the tree house window.

“Books!” she shouted.

“What?”

“It’s filled with books!”

Oh, man! Jack loved books.

He pushed his glasses into place. He gripped the sides of the rope ladder, and up he went.