Isaac was a curious fifth-grader who loved solving puzzles and mysteries. One day, when he arrived at his desk in the classroom, he noticed that his favorite pen was missing. He searched high and low, but the pen was nowhere to be found.

Determined to get to the bottom of this mystery, Isaac began to investigate. He started by asking his classmates if they had seen his pen, but no one seemed to know what had happened to it. Undeterred, Isaac decided to gather some clues.

He carefully examined his desk, looking for any signs that could help him solve the case. Suddenly, he noticed a small piece of paper hidden underneath his notebook. Upon closer inspection, he realized it was a note written in a strange, unfamiliar handwriting.

The note read, "If you want to see your pen again, meet me at the school library after class." Isaac's heart raced with excitement. He had a lead, and he was determined to follow it.

After the final bell rang, Isaac hurried to the library, his mind racing with possibilities. As he approached the library door, he saw a shadowy figure waiting inside. Cautiously, he entered the room, ready to confront the person who had taken his pen.