en, while the wheels squelched through the mud
below, and the rain beat rhythmically on the windows and roof of the
cab. Its noise seemed to ally itself to the interior smell of the
vehicle, an odor of damp leather and stale straw and ancient stables.
The Professor stared intently through the wet glass, and Mary
remembered, with a touch of amusement, her first meeting with him,
when she had sat beside him and occupied her thoughts with the flabby
phantom of Smith.

"You know," she said, at length, "there'll have to be some sort of
explanation."

"Well?" demanded the Professor.

"If I knew what you had done to Mr. Smith," she went on, "I could
help you to keep things as quiet as possible."

He heard her with a frown and shook his head. "If you knew, you'd do
anything but keep it quiet," he answered shortly.

"Then it was something horrible?" asked Mary quickly.

He smiled. "I expect to have many patients for the same treatment,"
he replied. "Very many; I expect half the world. Where is Smith now?"
he asked abruptly.

"At home by himself," replied Mary. "We'll be there in two minutes.
You'd like to see him first?"

"Yes, please," he said. "I must have a word or two with him."

Dr Pond had not returned when they drew up at the house, and, as soon
as the Professor had rid himself of his ulster and hat, she led him
upstairs to the "study."

"You'll find him in here," she said, when they came to the door. "I
shall be downstairs when you want me."

The Professor nodded absently and turned the handle. Mary was at the
top of the stairs when he entered. She turned even before he cried
out, conscious of something happening.

"Stop!" cried the Professor sharply. "Put that down!"

Mary ran to the open door and uttered a cry. Near the window stood
Smith, erect and buoyant. The contents of desk-drawers were littered
on the floor--papers, old pipes, a corkscrew, various rubbish--and in
his hand he held something that Mary recognized with a catch of the
breath.

"Father's old pistol!" she said, and shuddered. The Professor had
advanced as far as the middle of the room; the desk was between him
and Smith, who was looking at him with a smile. Even in the weakness
of fear that came over her, Mary wondered at the change in him. His
very stature seemed to be greater; there was a grave power in that
face she knew as a mask of witlessness and futility. He held the
revolver in his right hand with the barrel resting in his lef