He turned on the wall switch and tuned in. There was a prolonged humming.

“… concludes the program of Christmas carols,” said the radio.

“A very nice tone,” said Fox approvingly.

“Here’s something sir,” announced Bailey suddenly.

“Found the sawdust, have you?” said Alleyn.

“Got it in one,” said the startled Bailey.

Alleyn peered into the instrument, using the torch. He scooped up two tiny traces of sawdust from under the holes.

“Vantage number one,” said Alleyn. He bent down to the wall plug. “Hullo! A two-way adapter. Serves the radio and the radiator. Thought they were illegal. This is a rum business. Let’s have another look at those knobs.”

He had his look. They were the usual wireless fitments, bakelite knobs fitting snugly to the steel shafts that projected from the front panel.

“As you say,” he murmured, “quite in order. Wait a bit.” He produced a pocket lens and squinted at one of the shafts. “Ye-es. Do they ever wrap blotting-paper round these objects, Fox?”

“Blotting-paper!” ejaculated Fox. “They do not.”

Alleyn scraped at both the shafts with his penknife, holding an envelope underneath. He rose, groaning, and crossed to the desk. “A corner torn off the bottom bit of blotch,” he said presently. “No prints on the wireless, I think you said, Bailey?”

“That’s right,” agreed Bailey morosely.

“There’ll be none, or too many, on the blotter, but try, Bailey, try,” said Alleyn. He wandered about the room, his eyes on the floor; got as far as the window and stopped.

“Fox!” he said. “A clue. A very palpable clue.”

“What is it?” asked Fox.

“The odd wisp of blotting-paper, no less.” Alleyn’s gaze traveled up the side of the window curtain. “Can I believe my eyes?”