"It seems such a particularly brutal and senseless crime," continued the other, after a short pause. "One would think that even the most callous ruffian would hesitate about striking down an old man of over eighty." He glanced at Colin's dressing gown. "I gather that the murderer broke into the house after you had gone to bed?" Colin was about to answer when the Inspector got up suddenly and turned toward the door. "We've seen all we want to for the present, doctor. Perhaps you'll be good enough to have a look at the body now, and let's hear your opinion?" The surgeon hurried forward, and, following him slowly into the room, Colin seated himself on the corner of the sofa. From this position he was able to watch the proceedings of all three of his companions, none of whom for the moment betrayed any desire to interrogate him further. Doctor Sinclair, after taking off his coat, became wholly absorbed in his professional duties. Marsden appeared to be busy making notes, while the sergeant, who had produced an electric torch and a large magnifying glass, stepped down into the garden and began a minute examination of the still open French window. At last, after a lapse of several minutes, the surgeon rose to his feet. "It is a clear case of deliberate murder," he said slowly. "The Professor was struck on the temple by some blunt weapon--probably a jemmy. There is no doubt that he was killed instantly. I should think he has been dead for about twenty minutes." The Inspector turned to Colin. "You were the first to view the body," he remarked. "Is there anything in the doctor's report with which you are not in agreement?" "Nothing," replied Colin. "I came to the same conclusion myself directly I examined the wound." Marsden pulled a chair up to the table, and the sergeant, who had been listening from the window, stepped forward and joined him. "I want the full facts now, Doctor Gray," he said brusquely. "Tell us in your own words exactly what happened from the moment you returned to the house." Amid a profound silence, broken only by the occasional scratching of the Inspector's pencil, Colin proceeded to relate his story. Starting with his talk to the Professor at the laboratory door, he went on step by step to describe the whole of his subsequent experiences right up to the arrival of his present companions. He kept strictly to the bare facts, making no attempt to explain his own views, and all three of his audience listened to him with an absorbed interest, which showed itself plainly in their faces. It was only when he had quite finished that the Inspector offered his first comment.