u, when it occurred to me that I hadn't noticed whether the
key had been left in or not."

"Did you go back to see?" asked Dr. Cairn.

"I didn't want to," admitted Crombie, "but I did--and--"

"Well?"

"The door was locked, sir!"

"So you concluded that your imagination had been playing you tricks,"
said Saunderson grimly. "In my opinion you were right."

Dr. Cairn dropped into an armchair.

"All right, Crombie; that will do."

Crombie, with a mumbled "Good-night, gentlemen," turned and left the
room.

"Why are you worrying about this matter," inquired Saunderson, when
the door had closed, "at a time like the present?"

"Never mind," replied Dr. Cairn wearily. "I must return to Half-Moon
Street, now, but I shall be back within an hour."

With no other word to Saunderson, he stood up and walked out to the
hall. He rapped at the study door, and it was instantly opened by
Robert Cairn. No spoken word was necessary; the burning question could
be read in his too-bright eyes. Dr. Cairn laid his hand upon his son's
shoulder.

"I won't excite false hopes, Rob," he said huskily. "I am going back
to the house, and I want you to come with me."

Robert Cairn turned his head aside, groaning aloud, but his father
grasped him by the arm, and together they left that house of shadows,
entered the car which waited at the gate, and without exchanging a
word _en route_, came to Half-Moon Street.

CHAPTER XXIV

FLOWERING OF THE LOTUS

Dr. Cairn led the way into the library, switching on the reading-lamp
upon the large table. His son stood just within the doorway, his arms
folded and his chin upon his breast.

The doctor sat down at the table, watching the other.

Suddenly Robert spoke:

"Is it possible, sir, is it possible--" his voice was barely
audible--"that her illness can in any way be due to the orchids?"

Dr. Cairn frowned thoughtfully.

"What do you mean, exactly?" he asked.

"Orchids are mysterious things. They come from places where there are
strange and dreadful diseases. Is it not possible that they may
convey--"

"Some sort of contagion?" concluded Dr. Cairn. "It is a point that I
have seen raised, certainly. But nothing of the sort has ever been
established. I have heard something, to-night, though, which--"

"What have you heard, sir?" asked his son eagerly, stepping forward to
the table.

"Never mind at the moment, Rob; let me think."

He rested his elbow upon the table, and his ch