"What to do next I did not know," continued the Professor. "I stood for a few moments horrified at my action. Suddenly it occurred to me that, being dressed exactly like me, it would be believed that I had been assaulted! But his features were not mine, so I took a bottle of highly corrosive acid and flung it into his face, and then exchanged my gold watch and keys for his, and put some of my letters into his pocket. Afterwards I replaced the one or two things that had been disordered in the laboratory, switched off the light, and, leaving the dead spy in the corner, closed both doors, which, as you will see, lock automatically." "And then?" I asked, amazed at his story. "Then I came in here, put a piece of plaster upon my finger, opened the safe, and took the precious books containing the records of my experiments, in order to make it appear that a robbery had been committed. After washing myself in my room, I strove to preserve an outward calm, and asked Ethelwynn to telephone for a sleeping-berth for me. I had now decided, as there was no further danger of spies, not to take her with me. Just before I left, I came in here and wrote her a letter, telling her I should be absent some months, and instructing her to call Kirk and regard him as her protector during my absence. As I went out I left the note beneath the salver on the hall table, so that it might be discovered by the maid when dusting in the morning. At 11:30 I left King's Cross for Edinburgh, without, however, being able to communicate with Kirk or tell him what had actually occurred." "I, on my part, naturally believed that the dead man was the Professor," Kirk interrupted. "And when were you aware of the truth?" I asked. "The day after I had called you in consultation. I then saw that, in exposing an affair which, at all hazards, must be kept a secret, I had acted most injudiciously. I did not dare to tell you the truth. I went to Edinburgh and found the Professor, who was in hiding, fearful lest the affair should be discovered. He told me exactly what had occurred, and invoked my aid. My agents watched every move you made. They were with you in Edinburgh and in Glasgow. Therefore, I was well aware how strenuously you were seeking a solution of the mystery." I paused in sheer amazement. As I reflected, I saw that Kirk had been shielding his friend the Professor all along. In reply to my questions, he told me that the reason why he could not satisfactorily prove an alibi if accused of the crime was because at the hour of the tragedy he was engaged upon a mission for the Government, a secret transaction with an agent of another foreign Power which was greatly to our advantage, and betrayal of which would create serious international complications. His allegations of enmity towards the Professor had been made to mystify me.