"You saw no one?" her son asked incredulously. "You heard nothing?"

"I heard no footsteps. I saw no one," Mrs. Rheinholdt repeated.

The Professor turned away.

"If you will allow me," he begged, "I am going to telephone to my friend
Mr. Sanford Quest, the criminologist. An affair so unusual as this might
attract him. You will excuse me."

The Professor hurried from the room. They brought Mrs. Rheinholdt more
champagne and she gradually struggled back to something like her normal
self. The dancing had stopped. Every one was standing about in little
groups, discussing the affair. The men had trooped towards the
conservatory, but the Professor met them on the portals.

[Illustration: "CONFESS THY SINS, MY GOOD MAN."]

[Illustration: THE BLACK BOX IS INTRODUCED INTO THE STORY.]

"I suggest," he said courteously, "that we leave the conservatory exactly
as it is until the arrival of Mr. Sanford Quest. It will doubtless aid him
in his investigations if nothing is disturbed. All the remaining doors are
locked, so that no one can escape if by any chance they should be hiding."

They all agreed without dissent, and there was a general movement towards
the buffet to pass the time until the coming of Mr. Sanford Quest. The
Professor met the great criminologist and his assistant in the hall upon
their arrival. He took the former at once by the arm.