"I am glad to see that," he said. "Whatever you do, don't disturb him. The more sleep he has the better."

"Mrs. Rent is sleeping, too," Ethel said.

"That is right," the doctor murmured. "I am sure she wants it. If we could only induce a sleep like this on the part of the patient oftener he would get better much the sooner. It is impossible for him to recover so long as he keeps on worrying his brain as he does. And now, at the risk of being impertinent, I am going to ask a personal question. I understand you have known Mr. Rent for a long time. Is that so?"

"I have known him all my life," Ethel said.

"Then you'll be able to tell me what I want to know. Of course, I recognise that he is an exceedingly clever man and that he has a very active and intelligent mind. I am told that he sits up half the night working out problems and fascinating experiments. These men make the most difficult patients when there is brain trouble. Tell me, do you think Mr. Rent has anything weighing heavily on his mind?"

Ethel hesitated. She was startled to find the doctor's train of thought very like her own. He put the question with a gravity which impressed her. But he was the doctor in charge of the case and had every right to the information of which he was in search.

"I am afraid so," she said. "It has been dawning upon me for the last day or two that there is something very wrong. Arnold Rent seems to be full of the idea that he has left some task unfinished. He is dreadfully afraid lest somebody should find out certain information which his illness prevented him from concealing. It may be that he has hit upon a new invention—something startling in the way of a discovery. On the other hand, it may be that he has done something to be ashamed of and does not want it known. I was going to ask his assistant, Mr. Swift, about the matter, but Mr. Rent never trusts him with anything of importance, because the latter has a weakness for drink. I feel pretty sure that the secret has something to do with a scientific discovery, because, a few minutes since, your patient was anxious to send for Mr. Malcolm Grey, a brother scientist. Then he suddenly changed his mind and told me to do nothing of the kind. I can't make it out at all."

The doctor looked grave.

"It is a most puzzling case," he said. "The best thing to do is to fall in with every wish the patient expresses. Never mind if he changes his opinion the next moment; humour him to the top of his bent, and don't disturb him in any case. The same remark applies to Mrs. Rent. Let the poor lady have all the rest she can get. I will look in again later."

The time passed slowly. It was growing late, and there was no sign of Mrs. Rent. Ethel sat in the sick-room waiting the advent of the doctor, who did not come, though it was now past eleven o'clock. Probably he had been detained somewhere. But, since Rent was slumbering in his chair, it did not matter. He moved uneasily in his sleep once or twice, and Ethel caught the name of Grey on his lips. Unconscious as he was, his mind was working away at the problem which puzzled him so sorely. Then Ethel closed her own eyes and for a little while was oblivious to all that was going on. When she came to herself she heard a clock striking the half-hour after eleven, so that she knew she had been asleep some five-and-twenty minutes. She wondered if her patient was awake, but was surprised to see that he was no longer seated in the chair. Possibly he had gone back to bed.