Quarles was professedly a theorist, and I admit that he often outraged my practical mind. I believe the practical people govern the affairs of the world, but occasionally one is brought face to face with such strange occurrences that it is impossible not to speculate what would happen had not the world its theorists and dreamers too. Early one morning about a week after the mad burglar's case, I received a wire from Zena Quarles, asking me to go to Chelsea as soon as possible. A request from her was a command to me, and, dispensing with breakfast, except for a hasty cup of coffee, I started at once. She came to the door herself. "Come in here for a minute," she said, leading the way into the dining-room and closing the door. "Grandfather does not know I have sent for you. I am troubled about him. For the last three days he has not left his room. He will not let me go to him. His door is not locked, but he commanded me, quite irritably, not to come until he called for me. For three days he has not wanted my companionship, and never before do I remember so long an isolation." "What is he doing?" I asked. She did not answer at once, and when she did the words came with some hesitation. "Of course, he is an extraordinary man, with powers which one cannot exactly define, powers which--don't think me foolish--powers which might prove dangerous. In a way, you and I understand him, but I think there is a region beyond into which we are not able to follow him. I admit there have been times when I have been tempted to think that some of his philosophical reasonings and fantastic statements were merely the eccentricities of a clever man--intentional mystifications, a kind of deceptive paraphernalia." "I have thought so too," I said. "We are wrong," she said decisively. "He wanders into regions into which we cannot follow--where he touches something which is outside ordinary understanding, and when he is only dimly conscious of the actualities about him. Don't you remember his saying once that we ought to strive toward the heights, and see the truth which lies behind what we call truth? He does climb there, I believe, and, in order that he may do so, his empty room and isolation are necessary. I wonder whether there is any peril in such a journey?" I did not venture to answer. Being a practical man, a discussion on these lines was beyond me. As I went to the professor's room I framed a knotty, if unnecessary, problem out of a case upon which I was engaged; but I was not to propound it. I was suddenly plunged into a mystery which led to one of the most curious investigations I have ever undertaken, and showed a new phase of the professor's powers. Christopher Quarles was sitting limply in the arm-chair, but he started as I entered, and looked at me with blinking eyes, as though he did not recognize me. Energy returned to him suddenly, and he sat up.