"No," replied Langton promptly; "both front and back doors are in Sussex Place. The door leading to the park was bricked up by the Professor, as he was always afraid that undesirable people might enter and steal the secrets of his experiments. There are two locked doors leading to the laboratory, of which he always keeps the keys. I'll show you them in a moment." And he led the way across the landing from the study to the boudoir. Here I noticed that the drawers of Miss Greer's little rosewood escritoire stood open, and that upon the table was a miscellaneous collection of odds and ends; letters, fancy needlework, and other things, as though a hasty search had been made among the dead girl's effects. To me it appeared that whoever had been making the investigation had been disturbed in the act and had escaped. The police noticed it, while Langton exclaimed: "Look! Ethelwynn is usually so very tidy! Somebody has, no doubt, been turning over her treasures. For what reason?" and he halted before the open door leading to the passage to the laboratory. "Look!" Inspector, sergeant, and constable all looked, but saw nothing unusual. The door stood open--that was all. "Don't you see!" cried the young man excitedly. "This door--the door which Professor Greer always keeps fastened--has been burst open. Somebody has been here! I was not mistaken after all!" And he made his way along the passage, opening the second door and entering the darkness of the great lofty room. The constable followed with his lamp, while I held behind, knowing that in a few seconds the ghastly truth must be discovered. Langton quickly found the switch, and the place was flooded with light. At the same moment a strong and pungent smell of some acid greeted our nostrils, causing us to catch our breath. It was due, we noticed, to a bottle of some liquid which had been knocked off the table nearest us, and lay smashed upon the tiled floor. Full of fear and trembling, I glanced to the corner in which I had seen the Professor's huddled-up body; but my heart gave a quick bound of joy. It was not there! Already evidences of the double tragedy had been removed. Was it for that reason, in order to remove them, that Kershaw Kirk had been there? "Why!" exclaimed Langton. "Look! the furnace is alight. The Professor certainly cannot be in Scotland!" I glanced to the left where he had indicated, and saw that the good-sized brick furnace built in the right-hand wall, in which, by means of a great electric fan, the Professor could generate, by forced draught, the intense heat he sometimes required for his experiments, was aglow. A fierce fire had evidently been burning there, but it was now slowly dying out. The warmth of the laboratory and of the brickwork of the furnace showed that the draught fan must have been used. "I wonder what the Professor has been doing to-day?" remarked the inspector, examining the place with considerable curiosity.