His investigation, which lasted all the morning, was careful and intelligent, but it led in the end to nothing.  He pointed out to us that there were two possible entrances to the museum which we had not considered.  The one was from the cellars by a trap-door opening in the passage.  The other through a skylight from the lumber-room, overlooking that very chamber to which the intruder had penetrated.  As neither the cellar nor the lumber-room could be entered unless the thief was already within the locked doors, the matter was not of any practical importance, and the dust of cellar and attic assured us that no one had used either one or the other.  Finally, we ended as we began, without the slightest clue as to how, why, or by whom the setting of these four jewels had been tampered with.

There remained one course for Mortimer to take, and he took it.  Leaving the police to continue their fruitless researches, he asked me to accompany him that afternoon in a visit to Professor Andreas.  He took with him the two letters, and it was his intention to openly tax his predecessor with having written the anonymous warning, and to ask him to explain the fact that he should have anticipated so exactly that which had actually occurred.  The Professor was living in a small villa in Upper Norwood, but we were informed by the servant that he was away from home.  Seeing our disappointment, she asked us if we should like to see Miss Andreas, and showed us into the modest drawing-room.

I have mentioned incidentally that the Professor’s daughter was a very beautiful girl.  She was a blonde, tall and graceful, with a skin of that delicate tint which the French call “mat,” the colour of old ivory, or of the lighter petals of the sulphur rose.  I was shocked, however, as she entered the room to see how much she had changed in the last fortnight.  Her young face was haggard and her bright eyes heavy with trouble.

“Father has gone to Scotland,” she said.  “He seems to be tired, and has had a good deal to worry him.  He only left us yesterday.”

“You look a little tired yourself, Miss Andreas,” said my friend.

“I have been so anxious about father.”

“Can you give me his Scotch address?”

“Yes, he is with his brother, the Rev. David Andreas, 1, Arran Villas, Ardrossan.”

Ward Mortimer made a note of the address, and we left without saying anything as to the object of our visit.  We found ourselves in Belmore Street in the evening in exactly the same position in which we had been in the morning.  Our only clue was the Professor’s letter, and my friend had made up his mind to start for Ardrossan next day, and to get to the bottom of the anonymous letter, when a new development came to alter our plans.

Very early on the following morning I was aroused from my sleep by a tap upon my bedroom door.  It was a messenger with a note from Mortimer.

“Do come round,” it said; “the matter is becoming more and more extraordinary.”