"I saw nothing whatever. But just as I approached the street door, I
heard a peculiar whistle, apparently proceeding from the gardens in the
center of the square. I attached no importance to it at the time."

"What kind of whistle?"

"I have forgotten the actual notes, but the effect was very odd in some
way."

"In what way?"

"An impression of this sort is not entirely reliable, Inspector; but it
struck me as Oriental."

"Ah!" said Dunbar, and reached out the long arm for his notebook.

"Can I be of any further assistance?" said Exel, glancing at his watch.

"You had entered the hall-way and were about to enter your own flat when
the voices of Dr. Cumberly and Mr. Leroux attracted your attention?"

"I actually had the key in my hand," replied Exel.

"Did you actually have the key in the lock?"

"Let me think," mused Exel, and he took out a bunch of keys and dangled
them, reflectively, before his eyes. "No! I was fumbling for the right
key when I heard the voices above me."

"But were you facing your door?"