It was exactly on the stroke of a quarter past three when, with a sharp blast from his horn, Colin shot past the policeman on duty and pulled up neatly in the centre court of Scotland Yard. Before he could attempt to dismount two indignant constables were alongside of him.
"Who are you?" demanded one. "Don't you know it's against the regulations to bring in a car without permission?"
"Sorry," said Colin penitently. "The fact is, I've got a very urgent appointment with Inspector Marsden. He telephoned me to be here at a quarter past without fail."
"Well, you take my advice and be a bit more careful the next time," observed his interrogator, "or as likely as not you'll find yourself in trouble." He turned to his companion. "Better take him up at once. The Inspector's in his room."
Climbing out of the car and following his guide, Colin ascended the flight of stone stairs until they reached the same apartment to which Marsden had conducted him before. Having inquired his name, the constable rapped loudly, and in answer to a peremptory invitation pushed open the door and stepped briskly forward.
"Doctor Gray to see you by appointment, sir."
Marsden blotted the letter that he was writing and got up from his desk.
"Come along in, doctor," he called out; and then, as Colin entered, he pulled forward a chair and motioned the constable to withdraw.
"Take that seat," he added, directly the door was shut. "There's no time to waste, and I want to hear your story before we discuss anything else. Don't hurry, though; tell it me in your own way, just as you did when you described the murder."
Colin laid his hat on the floor, and, thrusting his hands in his pockets, commenced to speak.