ng on the
walls, a chair or two, a couch half hidden from the detective's view, and
that was all. He had expected to see Odette Rider with her mother, and
was disappointed. Not only was Mrs. Rider alone, but she conveyed the
impression that she was practically alone in the house.

Tarling knelt, watching her, for ten minutes, until he heard a sound
outside. He crept softly back and looked over the edge of the portico in
time to see a figure moving swiftly along the path. It was riding a
bicycle which did not carry a light. Though he strained his eyes, he
could not tell whether the rider was man or woman. It disappeared under
the portico and he heard the grating of the machine as it was leant
against one of the pillars, the click of a key in the lock and the sound
of a door opening. Then he crept back to his observation post overlooking
the study.

Mrs. Rider had evidently not heard the sound of the door opening
below, and sat without movement still staring at the wall before her.
Presently she started and looked round towards the door. Tarling noted
the door--noted, too the electric switch just in view. Then the door
opened slowly. He saw Mrs. Rider's face light up with pleasure, then
somebody asked a question in a whisper, and she answered--he could just
hear her words:

"No darling, nobody."

Tarling held his breath and waited. Then, of a sudden, the light in the
room was extinguished. Whoever had entered had turned out the light.
He heard a soft footfall coming towards the window looking into the
conservatory and the rattle of the blinds as they were lowered. Then the
light went up again, but he could see nothing or hear nothing.

Who was Mrs. Rider's mysterious visitor? There was only one way to
discover, but he waited a little longer--waited, in fact, until he heard
the soft slam of a safe door closing--before he slipped again through the
window and dropped to the ground.

The bicycle was, as he had expected, leaning against one of the pillars.
He could see nothing, and did not dare flash his lamp, but his sensitive
fingers ran over its lines, and he barely checked an exclamation of
surprise. It was a lady's bicycle!

He waited a little while, then withdrew to a shrubbery opposite the door
on the other side of the drive up which the cyclist had come. He had not
long to wait before the door under the portico opened again and closed.
Somebody jumped on to the bicycle as Tarling leaped from his place of
conce