The point was not argued further.

"I may take it, then," suggested the Professor, "that we are prepared to start at once,"

"There's nothing to stop us," said Marring.

"Thasso," said Crantor.

The Professor turned and gazed thoughtfully out of the window. It looked very cold and bleak outside, but what he saw seemed to please him, for he smiled.

Three nights later, at about nine o'clock, Betty Tregarth was roused from the book she was reading by the ringing of the telephone.

"Is that Miss Betty Tregarth?"

"Yes. Who is that?"

"I am speaking for your brother, Miss Tregarth. My name is Raxel--Professor Bernhard Raxel. Your brother was knocked down by a taxi outside my house a little while ago, and he was carried in here to await the arrival of an ambulance. The doctors, however, have decided against moving him."

The girl's heart stopped beating for a moment.

"Is he--is he in danger?"

"I am afraid your brother is very seriously injured, Miss Tregarth, but he is quite conscious. Will you please come at once?"

"Yes, yes!" She was frantic now. "What address?"

Number seven, Cornwallis Read. It is onlya few hundred yards from your front door.'

"I know. I'll be round in five minutes. Goodbye."

She hung up the receiver and dashed for a' hat and coat.

Only an hour ago her brother had left the flat which they shared, having declared his intention of visiting a West End cinema. He would have passed down Cornwallis Road on his way to the tube station. She dared not think how bad his injuries might be. She knew the significance of these quietly ominous summonses, for her father had been fatally injured in a street accident only three years before.