It was a sunny afternoon in Oakwood Elementary, and the fifth-grade class was abuzz with excitement. The school's annual Science Fair was just around the corner, and everyone was busy preparing their projects. But for one student, Lily, the excitement quickly turned to confusion and mystery.

As Lily was setting up her display on the properties of water, she noticed that her prized collection of glass marbles had gone missing. She searched high and low, but the colorful spheres were nowhere to be found. Determined to solve the mystery, Lily enlisted the help of her best friend, Ethan.

"Someone must have taken them," Lily said, her brow furrowed in concentration. "But who could it be, and why would they want my marbles?"

Ethan and Lily began to investigate, questioning their classmates and scouring the science fair exhibits for any clues. They even enlisted the help of their teacher, Mrs. Walters, who promised to keep an eye out for the missing marbles.

Just when they were about to give up, Lily had a sudden realization. "Wait, Ethan! Remember that new student, Alex, who joined our class last week? He seemed really interested in my marbles earlier today."