The missing envelope

On Monday morning, Mr Tan, the head of science, discovered that a brown envelope had disappeared from his desk. It contained the mark scheme for Thursday's IGCSE mock exam.

Only one student had been in his office that weekend: Victor, the student council president, who had come to "drop off a report". Everyone suspected him, and Victor knew it. Taking the answers from a teacher's desk, with his name in the visitors' book, was an audacious move, the kind of risk most people would never dare to take.

Victor's record was impeccable. He had perfect grades, perfect attendance and a perfect smile. Teachers trusted him, which was exactly why he had been able to walk into the office alone.

On Tuesday, while Victor was in assembly, two teachers surreptitiously searched the student council room, making sure no one saw them. Their search was far from perfunctory. They opened every drawer, checked inside every folder, looked behind the radiator and even unscrewed the legs of the table. They searched his locker and his bag. Nothing.

At lunch, Victor sat down opposite Mr Tan in the canteen. "I heard there was a problem in your office, sir," he said, with a brazen calm, as if he had nothing to hide and wanted everyone to see it.

That afternoon, Mr Tan asked Lina for help. She was in Year 11, quiet, and known for noticing things other people missed. She was astute: she understood people quickly, often better than they understood themselves.

"They looked everywhere," Mr Tan said. "So where is it?"

Lina thought for a long moment. Then she gave a cryptic reply that Mr Tan didn't understand at all: "Maybe they looked too carefully."