"I think he's a quarter of a mile away by this time. All the same, until the police arrive the room mustn't be left unwatched for a single moment."
He waited until she had obeyed his instructions, and then, with a final glance round, walked swiftly down the passage and took off the receiver.
"Get me on to Scotland Yard as soon as possible," he said.
There was a note of urgency in his demand which must have carried conviction even to the mind of the clerk, for in something less than ten seconds the reply came.
"Scotland Yard speaking. Who's that?"
"Dr. Colin Gray. Can you tell me if Inspector Marsden is still there?"
"I think so. Hold on a minute and I'll find out."
A pause followed.
"Hullo!" exclaimed a voice. "I'm Marsden. What's the matter, doctor? I didn't expect to hear from you again at this time of night."
"It's a bad business," said Colin quietly. "I'm speaking from the Red Lodge, Campden Hill. I have just found Professor Carter lying dead in his study."