"I discovered the truth," he said in a hard, changed tone. "The doors gave us a good deal of trouble. At the end of the laboratory, huddled in a corner, was the body of the Professor. He had been stabbed to the heart, while his face presented a horrible sight, the features having been burned almost beyond recognition by some terribly corrosive fluid-- a crime which in every phase showed itself to be due to some fiendish spirit of revenge." "But that is most extraordinary!" I gasped, staring at the speaker. "The sleeping-car conductor took him to Edinburgh! Besides, how could the two doors be locked behind the assassin? Were the keys still upon the victim?" "They are still upon the dead man's watch-chain," he said. "But, mark you, there is still a further feature of mystery in the affair. After her father's departure for the station, his daughter put on a dressing-gown and, sending Morgan to bed, seated herself in her arm-chair before the fire in the Red Room, or boudoir, and took a novel. She read until past four o'clock, being in the habit of reading at night, and then, not being sleepy, sat writing letters until a drowsiness fell upon her. She did not then awake until a maid entered at seven to draw up the blinds." "Then she was actually at the only entrance to the laboratory all the night!" "Within a yard and a half of it," said Kershaw Kirk. "But the affair presents many strange features," he went on. "The worst feature of it all, Mr. Holford, is that a motive--a very strong motive--is known to certain persons why I myself should desire to enter that laboratory. Therefore I must be suspected of the crime, and--well, I admit at once to you I shall be unable to prove an alibi!" I was silent for a moment. "Unable to prove an alibi!" I echoed. "But the police have as yet no knowledge of the affair," I remarked. "No; I have, however, reported it in another quarter. It's a most serious matter, for I have suspicion that certain articles have been abstracted from the laboratory." "And that means--what?" "It means, my dear sir, very much more than you ever dream. This is at once the strangest and the most serious crime that has been committed in England for half a century. You are a man of action and of honour, Mr. Holford. Will you become my friend, and assist me in trying to unravel it?" he asked quickly, bending forward to me in his earnestness. "Most certainly I will," I replied, fascinated by the amazing story he had just related, quite regardless of the fact that he was the suspected assassin. I wonder whether if I had known into what a vortex of dread, suspicion, and double-dealing that decision of mine would have led me I would have so lightly consented to render my help? I think not.