“I got there just as the other taxi was drawing up in front of the hotel.  A porter came forward and opened the door, and I saw the man get out and go up the steps.  I waited for one moment, and then I walked along to the entrance myself.  The porter was still standing there, so I went straight up to him and asked him quite simply what the name of the gentleman was who had just gone inside.  He sort of hesitated, and then he said to me:  ’That gentleman, Miss?—­that’s Dr. McMurtrie.’”

Once more she paused, and, pushing away the tray, I lit myself a cigar.  “It’s lucky you’ve had some practice in surprises,” I observed.

Joyce nodded.  “Of course I was absolutely flabbergasted, but I don’t think I showed anything.  I sort of rummaged in my bag for a minute till I’d recovered; then I gave the man half a crown and asked him if he knew how long Dr. McMurtrie was staying.  I think he was in doubt as to whether I was a female detective or a lady reporter; anyhow he took the money and said he was very sorry he didn’t know, but that if I wanted an interview at any time he had no doubt it might be arranged.  I thanked him, and said it didn’t matter for the moment, and there I thought it best to leave things.  You see I knew that whether McMurtrie stayed on at the Russell or not you were bound to see him again, and there was nothing to be gained by asking questions which the porter would probably repeat to him.  It would only have helped to put him on his guard—­wouldn’t it?”

“My dear Joyce,” I said, “I think you did splendidly.  Sherlock Holmes couldn’t have done better.”  I got up and walked to the end of the cockpit.  “But good Lord!” I added, “this does complicate matters.  You’re absolutely certain it was McMurtrie you saw at Marks’s flat?”

“Absolutely,” repeated Joyce with emphasis.  “I should remember his face if I lived to be a hundred.”

I clenched my fists in a sudden spasm of anger.  “There’s some damned villainy underneath all this, Joyce,” I said.  “If McMurtrie was there that afternoon the odds are that he knows who committed the murder.”

“He did it himself,” said Joyce calmly.  “I’m as sure of it as I am that I’m sitting here.”

“But why?” I demanded—­“why?  Who on earth was Marks?  Nobody in Chelsea seemed to know anything about him, and nothing came out at the trial.  Why should any one have wanted to kill him except me?”

Joyce shook her head.  “I don’t know,” she said stubbornly; “but I’m quite certain it was McMurtrie.  I feel it inside me.”

“And in any case,” I continued, “what the devil is he doing messing about with George?  I’m the only connecting-link between them, and he can’t possibly mean to betray me—­at all events, until he’s got the secret of the powder.  He knows George would give me up tomorrow.”

Joyce made a gesture of perplexity.  “I know,” she said.  “It’s an absolute mystery to me too.  I’ve been puzzling and puzzling over it till my head aches, and I can’t see any sort of explanation at all.”