“Good.” Antony put his hand into the space left by the stout Ussher, and fingered the back of the shelf. “Pull,” he said.

Bill pulled.

“Now just go on pulling like that. I shall get it directly. Not hard, you know, but just keeping up the strain.”

His fingers went at it again busily.

And then suddenly the whole row of shelves, from top to bottom, swung gently open towards them.

“Good Lord!” said Bill, letting go of the shelf in his amazement.

Antony pushed the shelves back, extracted Ussher from Bill’s fingers, replaced him, and then, taking Bill by the arm, led him to the sofa and deposited him in it. Standing in front of him, he bowed gravely.

“Child’s play, Watson,” he said; “child’s play.”