Their employees had all been with them many years, and it was easy to find the two men who had worked under Mr. Marsh’s orders. They remembered the job perfectly. Amongst various other minor jobs, they had taken up one of the bricks of the old-fashioned fireplace, made a cavity beneath, and so cut the brick that it was impossible to see the join. By pressing on the second brick from the end, the whole thing was raised. It had been quite a complicated piece of work, and the old gentleman had been very fussy about it. Our informant was a man called Coghan, a big, gaunt man with a grizzled moustache. He seemed an intelligent fellow.

We returned to Crabtree Manor in high spirits, and, locking the study door, proceeded to put our newly acquired knowledge into effect. It was impossible to see any sign on the bricks, but when we pressed in the manner indicated, a deep cavity was at once disclosed.

Eagerly Poirot plunged in his hand. Suddenly his face fell from complacent elation to consternation. All he held was a charred fragment of stiff paper. But for it, the cavity was empty.