“And who was the patient?” rapped Smith.

“According to the woman’s account, the patient was her mother, who had met with a street accident a week before.  She gave the name of the consultant who had been called in, and who, she stated, had advised the opinion of Sir Baldwin.  She represented that the matter was urgent, and that it might be necessary to perform an operation immediately in order to save the patient’s life.”

“But surely,” I interrupted, in surprise, “Sir Baldwin did not take his instruments?”

“He took his case with him—­yes,” replied Logan; “for he in turn yielded to the appeals of the visitor.  The very last words that I heard him speak as he left the house were to assure her that no such operation could be undertaken at such short notice in that way.”

Logan paused, looking around at us a little wearily.

“And what aroused your suspicions?” said Smith.

“My suspicions were aroused at the very moment of Sir Baldwin’s departure, for as I came out onto the steps with him I noticed a singular thing.”

“And that was?” snapped Smith.

“Directly Sir Baldwin had entered the cab the woman got out,” replied Logan with some excitement in his manner, “and reclosing the door took her seat beside the driver of the vehicle—­which immediately moved off.”

Nayland Smith glanced significantly at me.

“The cab trick again, Petrie!” he said; “scarcely a doubt of it.”  Then, to Logan:  “Anything else?”

“This,” replied the secretary:  “I thought, although I could not be sure, that the face of Sir Baldwin peered out of the window for a moment as the cab moved away from the house, and that there was strange expression upon it, almost a look of horror.  But of course as there was no light in the cab and the only illumination was that from the open door, I could not be sure.”

“And now tell Mr. Smith,” said Weymouth, “how you got confirmation of your fears.”

“I felt very uneasy in my mind,” continued Logan, “for the whole thing was so irregular, and I could not rid my memory of the idea of Sir Baldwin’s face looking out from the cab window.  Therefore I rang up the consultant whose name our visitor had mentioned.”

“Yes?” cried Smith eagerly.

“He knew nothing whatever of the matter,” said Logan, “and had no such case upon his books!  That of course put me in a dreadful state of mind, but I was naturally anxious to avoid making a fool of myself and therefore I waited for some hours before mentioning my suspicions to any one.  But when the morning came and no message was received I determined to communicate with Scotland Yard.  The rest of the mystery it is for you, gentlemen, to unravel.”

CHAPTER XVI

I TRACK ZARMI