“But what about your fiancé’s arrest?” asked Henry. “You see, that provides him with an excellent motive, if I may say so, for murdering your father. But the police don’t work on motive alone, you know. They want proof of opportunity to commit a crime. And in this case there are two crimes.”

“Three,” corrected his sister, and read from the newspaper before her an account of the death of Dr. Crocker, which had taken place the night before. Henry looked at her aghast.

“You see,” went on Violet Arnell, “it’s not merely that Harry had a reason for putting father out of the way. He inherited some money from Dr. Wilkinson, who was a distant relative of his. That was what put the police on his track, I think.”

“Even so,” murmured Henry thoughtfully, “that’s no real reason why he should be arrested. Motive in the two cases would not be enough alone. They must have more to go on than that.”

“They have,” Violet explained somewhat grimly. “Harry was outside the British Museum last night, at the time when the murder was committed.”

“Good Lord!” Henry Fairhurst did not often permit himself the use of strong language of this sort, but he felt that this was a privileged occasion.

“How on earth,” he asked, when he had recovered his equanimity, “was he such a fool as to venture there last night?”

“That’s really what I’ve come to you about, Mr. Fairhurst,” replied the girl. “Last night Harry was going to see me. After he had finished correcting some examination papers at school he had promised to call around and see me. But while I was at tea a note from him was brought round by one of the boys. This is it.” She fumbled in her handbag and produced a letter which she passed over to Mr. Fairhurst, who, conscious that his sister was craning her neck in a vain effort to peer over his shoulder and read it, proceeded to read its contents aloud.

“Dear Violet,” the note said, “I’m afraid that I shan’t be able to come tonight. I’ve received a most mysterious missive, telling me to be outside the British Museum from midnight onwards. It hints that there will be developments with regard to the death of your father. I suspect that the police are going to try out something. Anyhow, my dear, I must be there, so I’m going straight up to town when school ends. Will give you a ring in the morning and tell you all about it. Wish me luck. Love. Harry.”