"I thought of that; but I don't believe anybody could guess so
accurately. For instance, how did he know about those letters?"

"Fact is," broke in Grady, "that's the first I'd heard of 'em. What
_is_ that story?"

I told him the story briefly, carefully suppressing everything which
would give him a clue to the identity of the veiled lady.

"There were certain details," I added, "which I supposed were known
to no one except myself and two other persons--and yet M. Pigot knew
them. Then again, how did he know so certainly just how the mechanism
worked? How did he know which roll of cotton contained that Mazarin
diamond? You will remember he told us what was in that roll before he
opened it."

Grady smiled good-naturedly and a little patronisingly.

"That was the last roll, wasn't it?" he demanded. "Since that big
diamond hadn't shown up in any of the others, he knew it had to be in
that roll. It was just one of the little plays for effect them
Frenchies are so fond of."

"Perhaps you are right," I agreed. "But it seemed to me that he
handled that mechanism as though he was familiar with it. Of course,
he may have prepared himself by studying the drawings which no doubt
accompany the secret memoir. He may even have had a working model
made."

Grady nodded tolerantly.