Caranby's mansion blocks any exit at the back. Anyone leaving
the house must go up the lane or through that part at the
bottom. The policeman was near there shortly before eleven
and saw no one leaving the house."

"But, look here," said Mr. Octagon, who had been ruminating;
"if, as the doctor says, death was instantaneous, how could
your aunt have rung the bell?"

"Yes," added Juliet. "And even had death not taken place at
once, it could not have been more than a few minutes before
eleven when the blow was struck. Aunt might have had strength
to crawl to the bell and touch it, but the assassin could not
have escaped from the house, seeing--as you say--the
policeman was on guard."

"Aunt died instantaneously," insisted Basil.

"Then she could not have sounded the bell," said Juliet
triumphantly.

"The assassin did that," said Peter.

"And thus called a witness," cried Basil. "Ridiculous!"

"Then how do you explain the matter?"

"I can't explain. Neither can the detective Jennings. It's a
mystery."