The inspector produced a pocket torch and flashed it along the sill outside.

“This is the way he went all right,” he remarked, “ and got in. See here.”

In the light of the powerful torch, several clearly defined footmarks could be seen. They seemed to be those of shoes with rubber studs in the soles. One particularly clear one pointed inwards, another, slightly overlapping it, pointed outwards.

“Plain as a pikestaff,” said the inspector. “Any valuables missing?”

Geoffrey Raymond shook his head. “Not so far that we can discover. Mr. Ackroyd never kept anything of particular value in this room.”