"Thanks so much," he exclaimed. "Now I think the best thing you can do is to get back to your room. I expect the police will want to see you when they come, but until then——"

Mrs. Ramsay shook her head.

"It wouldn't be no use, sir. I couldn't close my eyes, not if you was to offer me a thousand pounds." She turned again toward the stairs. "Besides, there's Mrs. Wilson—the cook, you know, sir. I've got to go and look after her."

"What's the matter? Is she ill?" demanded Colin.

"I heard her screaming," was the answer. "I shouldn't wonder if anything had happened, what with being woke up sudden and her having a weak heart."

"People don't often die from shock," said Colin. "Take her up a drop of brandy out of the dining room, and you had better have a little yourself at the same time."

He thrust his feet into the slippers, and, putting on his dressing gown, reentered the study.

Unlike most people whose ideas on the subject are drawn chiefly from sensational novels, Colin knew that the surest way of assisting a criminal was for some well-meaning amateur to conduct a few preliminary investigations before the arrival of the police. During his four years at the hospital he had twice been called upon to give evidence in cases of murder, and the experience had convinced him that it was only when a properly qualified detective was first in the field that any really valuable clues were likely to be forthcoming. Marsden's urgent instructions over the telephone had therefore been unnecessary; even without them he would certainly have waited for the Inspector's appearance before attempting any further interference with the existing condition of the room.

He walked across to where the Professor was lying and looked down again at the body. The sight filled him with a mingled grief and anger that were almost unbearable. He had revered the dead man with all the ardour of a disciple, and, in addition to this lifelong homage, their close intimacy during the last few weeks had produced other and still stronger ties. In spite of the old scientist's rather dictatorial manner, his attitude throughout had been so extraordinarily kind and generous that a very real if half-unconscious affection for him had gradually sprung up in Colin's heart. The thought that the murder had been committed while he was actually in the house only increased the horror and bitterness of the whole affair. No excuses could alter his feeling that he had failed miserably—failed in the very duty for which he had been selected and employed.

Self-reproaches, however, were of little use now, and with a tremendous effort he wrenched his mind back to the immediate problem that confronted it. Why, in God's name, should any one have wished to kill the Professor, and how had it come about that the latter's body was lying where it did? In order to reach the study from the laboratory one had to pass through the whole length of the hall. Colin's hearing was particularly acute, and he felt positive that the creak of footsteps or the opening or shutting of a door would instantly have attracted his attention. Nothing of the sort had happened. Until that one crash of breaking glass the whole house had been absolutely silent.