The Mystery of the Open Window

For three weeks now, the classroom window had been open every morning. Mr Halpern, the teacher, was puzzled.

"I lock that window every evening," he said. "Every. Single. Evening."

He held up the key.

"And yet — open."

The class looked at the window. It was the small high window at the back, the one with the broken latch.

Pim wrote in his notebook:

Case Number 7: The Open Window.

He raised his hand.

"Can I investigate?"

Mr Halpern was a good sport about Pim's detective work. "Yes, but please don't break anything else."

That morning at break, while the others played, Pim stayed behind. He looked at the window. He looked at the floor under the window.

There was — a very tiny smudge of something on the windowsill. Pim leaned closer. The smudge looked like dirt. But it was small. Very small. Pim's finger was bigger than the smudge.

He looked at the floor. There were three more tiny smudges, in a small, uneven line, leading from the window to the bookshelf.

The smudges stopped at the bookshelf.

Pim got down on his hands and knees. He shone his torch (a detective always carries a torch) under the bookshelf.

A pair of tiny black eyes stared back.

"Aha," said Pim, very quietly.