a law with me to have conviction forced upon me.  I do not believe unusual things until investigation proves them.  I am making an exception in the case of Shan Tung.  I have never regarded him as a man, like you and me, but as a sort of superphysical human machine possessed of a certain psychological power that is at times almost deadly.  Do you begin to understand me?  I believe that he has exerted the whole force of that influence upon Miriam Kirkstone—­and she has surrendered to it.  I believe—­and yet I am not positive.”

“And you have watched them for six months?”

“No.  The suspicion came less than a month ago.  No one that I know has ever had the opportunity of looking into Shan Tung’s private life.  The quarters behind his cafe are a mystery.  I suppose they can be entered from the cafe and also from a little stairway at the rear.  One night—­very late—­I saw Miriam Kirkstone come down that stairway.  Twice in the last month she has visited Shan Tung at a late hour.  Twice that I know of, you understand.  And that is not all—­quite.”

Keith saw the distended veins in McDowell’s clenched hands, and he knew that he was speaking under a tremendous strain.

“I watched the Kirkstone home—­personally.  Three times in that same month Shan Tung visited her there.  The third time I entered boldly with a fraud message for the girl.  I remained with her for an hour.  In that time I saw nothing and heard nothing of Shan Tung.  He was hiding—­or got out as I came in.”

Keith was visioning Miriam Kirkstone as he had seen her in the inspector’s office.  He recalled vividly the slim, golden beauty of her, the wonderful gray of her eyes, and the shimmer of her hair as she stood in the light of the window—­and then he saw Shan Tung, effeminate, with his sly, creeping hands and his narrowed eyes, and the thing which McDowell had suggested rose up before him a monstrous impossibility.

“Why don’t you demand an explanation of Miss Kirkstone?” he asked.

“I have, and she denies it all absolutely, except that Shan Tung came to her house once to see her brother.  She says that she was never on the little stairway back of Shan Tung’s place.”

“And you do not believe her?”

“Assuredly not.  I saw her.  To speak the cold truth, Conniston, she is lying magnificently to cover up something which she does not want any other person on earth to know.”

Keith leaned forward suddenly.  “And why is it that John Keith, dead and buried, should have anything to do with this?” he demanded.  “Why did this ‘intense interest’ you speak of in John Keith begin at about the same time your suspicions began to include Shan Tung?”

McDowell shook his head.  “It may be that her interest was not so much in John Keith as in you, Conniston.  That is for you to discover—­tonight.  It is an interesting situation.  It has tragic possibilities.  The instant you substantiate my suspicions we’ll deal directly with Shan Tung.  Just now—­there’s Wallie behind you grinning like a Cheshire cat.  His dinner must be a success.”