small apartment in which Stuart saw his patients. Dunbar looked slowly
about him, standing in the middle of the room, then crossed and stared
out of the window into the narrow lane below.

"Where were you when he gave you the envelope?" he snapped suddenly.

"At the table," replied Stuart with surprise.

"Was the table-lamp alight?"

"Yes. I always light it when seeing patients."

"Did you take the letter into the study to seal it in the other
envelope?"

"I did, and he came along and witnessed me do it."

"Ah," said Dunbar, and scribbled busily in his note-book. "We are
badly tied at Scotland Yard, doctor, and this case looks like being
another for which somebody else will reap the credit. I am going to
make a request that will surprise you."

He tore a leaf out of the book and folded it carefully.

"I am going to ask you to seal up something and lock it away! But I
don't think you'll be troubled by cowled burglars or beautiful women
because of it. On this piece of paper I have written--_a"_--he ticked
off the points on his fingers: "what I believe to be the name of the
man who cut out the cardboard and sealed it in an envelope; _b_: the
name of the cabman; and, _c_: the name of the man who rang me up here