Just pausing to gather his dressing gown about him, he hurried down the passageway to the outer door, which he unfastened and opened. A large car was drawn up in the roadway, and five men, two of them uniformed constables, were standing in a group on the pavement. Inspector Marsden, who was in the centre, immediately came forward. "Well, what's happened, doctor?" he inquired curtly. "Anything fresh to report?" Colin shook his head. "Only what I told you over the telephone," he replied. "The Professor is dead, and the man who murdered him has escaped." "That's enough to go on with, anyhow," returned the detective. "Jackson, you and Roberts stop here for the present. If any one attempts to leave the house arrest them at once." With an obedient salute the two constables fell back, and, followed by his other companions, Marsden mounted the steps. "This is Doctor Sinclair, our divisional surgeon," he announced. "He tells me that he has already had the pleasure of meeting you." Colin shook hands with a tall, gray-bearded man, whose face seemed vaguely familiar. "And this," continued the Inspector, "is Detective Sergeant Humphries, of the Finger Print Department. Now I think the first thing we'll do is to go in and have a look at the body. I'll take your statement as soon as the doctor has finished his examination." Without offering any comment, Colin conducted them down the corridor, and, leading the way across the hall, brought them to the door of the study. Marsden halted in the entrance, and stood staring silently at the tragic spectacle in front of him. "You followed my instructions?" he asked. "Everything is exactly as you found it!" "Exactly," said Colin. "Then I'll ask you two gentlemen to wait here for a moment. There's just one point I should like to make certain about before any one touches the body." He pulled out a notebook from his inside pocket, and, beckoning to his colleague stepped forward into the room. Doctor Sinclair moved across to where Colin was standing. "I don't suppose you remember me," he said, "but I called in at St. Christopher's last year in connection with one of your cases." He nodded toward the two detectives, both of whom were kneeling down beside the dead man. "This is a very terrible business," he added. "I was horrified when I heard that it was Professor Carter." Colin, whose mind was in no state for conversation, made an effort to collect his thoughts. "Did you know him personally?" he asked. The surgeon shook his head. "No," he replied. "Like everyone else, I was a great admirer of his work, but I never had the honour of being introduced to him. The police tell me that you were acting as his resident assistant." "I came here straight from the hospital," said Colin. "I had been with him for nearly a month."