The characters were a young man and a girl. The girl was extremely
pretty and very pale. The man was the exact double of Frank Merrill. He
was dressed in a rough tweed suit, and wore a soft felt hat with a
fairly wide brim. But it was not the appearance of this remarkable
apparition which startled the investigator. It was the attitude of the
two people. The girl was evidently pleading with her companion. Saul
Arthur Mann was too far away to hear what she said, but he saw the
young man shake himself loose from the girl. She again grasped his arm
and raised her face imploringly.

Mr. Mann gasped, for he saw the young man's hand come up and strike her
back into the house. Then he caught hold of the door and banged it
savagely, walked down the stairs, and, turning, hurried away.

The investigator stood as though he were rooted to the spot, and before
he could recover himself the fellow had turned the corner of the road
and was out of sight. Saul Arthur Mann took off his hat and wiped his
forehead. All his initiative was for the moment paralyzed. He walked
slowly up to the gate and hesitated. What excuse could he have for
calling? If this were Frank, assuredly his own views were all wrong, and
the mystery was a greater mystery still.

His energies began to reawaken. He took a note of the number of the
house, and hurried off after the young man. When he turned the corner
his quarry had vanished. He hurried to the next corner, but without
overtaking the object of his pursuit. Fortunately, at this moment, he
found an empty taxicab and hailed it.

"Grimm's Hotel, Jermyn Street," he directed.

At least he could satisfy his mind upon one point.

CHAPTER XV

A LETTER IN THE GRATE

Grimm's Hotel is in reality a block of flats, with a restaurant
attached. The restaurant is little more than a kitchen from whence meals
are served to residents in their rooms. Frank's suite was on the third
floor, and Mr. Mann, paying his cabman, hurried into the hall, stepped
into the automatic lift, pressed the button, and was deposited at
Frank's door. He knocked with a sickening sense of apprehension that
there would be no answer. To his delight and amazement, he heard Frank's
firm step in the tiny hall of his flat, and the door was opened. Frank
was in the act of dressing for dinner.

"Come in, S. A. M.," he said cheerily, "and tell me all the news."

He led the way back to his room and resumed the delicate task of tying
his dre