His escaped prisoner had turned the key on the outside. He was locked
in his own study!

Momentarily nonplussed, he stood looking at the closed door. The sound
of a restarted motor from outside the house spurred him to action. He
switched off the lamps, crossed the darkened room and drew back the
curtain, throwing open the French windows. Brilliant moonlight bathed
the little lawn with its bordering of high privet hedges. Stuart ran
out as the sound of the receding car reached his ears. By the time
that he had reached the front of the house the street was vacant from
end to end. He walked up the steps to the front door, which he
unfastened with his latch-key. As he entered the hall, Mrs. M'Gregor
appeared from her room.

"I did no' hear ye go out with Miss Dorian," she said.

"That's quite possible, Mrs. M'Gregor, but she has gone, you see."

"Now tell me, Mr. Keppel, did ye or did ye no' hear the wail o' the
pibroch the night?

"No--I am afraid I cannot say that I did, Mrs. M'Gregor," replied
Stuart patiently. "I feel sure you must be very tired and you can
justifiably turn in now. I am expecting no other visitor. Good-night."

Palpably dissatisfied and ill at ease, Mrs. M'Gregor turned away.

"Good-night, Mr. Keppel," she said.

Stuart, no longer able to control his impatience, hurried to the study