“How dare you contradict me, sir!” he cried, slapping the table sharply with his open hand.  “I was not here on Monday.”

The manager shrugged his shoulders coldly.

“You forget that the attendants also saw you,” he remarked.  “Cannot we trust our own eyes?”

“A common assumption, yet not always a strictly reliable one,” insinuated Carrados softly.

“I cannot be mistaken.”

“Then can you tell me, without looking, what colour Professor Bulge’s eyes are?”

There was a curious and expectant silence for a minute.  The professor turned his back on the manager and the manager passed from thoughtfulness to embarrassment.

“I really do not know, Mr. Carrados,” he declared loftily at last.  “I do not refer to mere trifles like that.”

“Then you can be mistaken,” replied Carrados mildly yet with decision.

“But the ample hair, the venerable flowing beard, the prominent nose and heavy eyebrows—­”

“These are just the striking points that are most easily counterfeited.  They ‘take the eye.’  If you would ensure yourself against deception, learn rather to observe the eye itself, and particularly the spots on it, the shape of the finger-nails, the set of the ears.  These things cannot be simulated.”

“You seriously suggest that the man was not Professor Bulge—­that he was an impostor?”

“The conclusion is inevitable.  Where were you on Monday, Professor?”

“I was on a short lecturing tour in the Midlands.  On Saturday I was in Nottingham.  On Monday in Birmingham.  I did not return to London until yesterday.”

Carrados turned to the manager again and indicated Draycott, who so far had remained in the background.

“And this gentleman?  Did he by any chance come here on Monday?”

“He did not, Mr. Carrados.  But I gave him access to his safe on Tuesday afternoon and again yesterday.”

Draycott shook his head sadly.

“Yesterday I found it empty,” he said.  “And all Tuesday afternoon I was at Brighton, trying to see a gentleman on business.”

The manager sat down very suddenly.

“Good God, another!” he exclaimed faintly.

“I am afraid the list is only beginning,” said Carrados.  “We must go through your renters’ book.”

The manager roused himself to protest.

“That cannot be done.  No one but myself or my deputy ever sees the book.  It would be—­unprecedented.”

“The circumstances are unprecedented,” replied Carrados.

“If any difficulties are placed in the way of these gentlemen’s investigations, I shall make it my duty to bring the facts before the Home Secretary,” announced the professor, speaking up to the ceiling with the voice of a brazen trumpet.

Carrados raised a deprecating hand.

“May I make a suggestion?” he remarked.  “Now, I am blind.  If, therefore—?”