Was he satisfied?  Certainly the event, puerile as it might seem to some, had opened up strange vistas to his aroused imagination.  The words “Edith, you know I promised you—­” were in themselves provocative of strange and doubtful conjectures.  Had the sleeper under the influence of a strain of music indissolubly associated with the death of Miss Challoner, been so completely forced back into the circumstances and environment of that moment that his mind had taken up and his lips repeated the thoughts with which that moment of horror was charged?  Sweetwater imagined the scene—­saw the figure of Brotherson hesitating at the top of the stairs—­saw hers advancing from the writing-room, with startled and uplifted hand—­heard the music—­the crash of that great finale—­and decided, without hesitation, that the words he had just heard were indeed the thoughts of that moment.  “Edith, you know I promised you—­” What had he promised?  What she received was death!  Had this been in his mind?  Would this have been the termination of the sentence had he wakened less soon to consciousness and caution?

Sweetwater dared to believe it.  He was no nearer comprehending the mystery it involved than he had been before, but he felt sure that he had been given one true and positive glimpse into this harassed soul which showed its deeply hidden secret to be both deadly and fearsome; and happy to have won his way so far into the mystic labyrinth he had sworn to pierce, he rested in happy unconsciousness till morning when—­

Could it be?  Was it he who was dreaming now, or was the event of the night a mere farce of his own imagining?  Mr. Brotherson was whistling in his room, gaily and with ever increasing verve, and the tune which filled the whole floor with music was the same grand finale from William Tell which had seemed to work such magic in the night.  As Sweetwater caught the mellow but indifferent notes sounding from those lips of brass, he dragged forth the music-box he held hidden in his coat pocket, and flinging it on the floor stamped upon it.

“The man is too strong for me,” he cried.  “His heart is granite; he meets my every move.  What am I to do now?”

XIX

THE DANGER MOMENT

For a day Sweetwater acknowledged himself to be mentally crushed, disillusioned and defeated.  Then his spirits regained their poise.  It would take a heavy weight indeed to keep them down permanently.

His opinion was not changed in regard to his neighbour’s secret guilt.  A demeanour of this sort suggested bravado rather than bravery to the ever suspicious detective.  But he saw, very plainly by this time, that he would have to employ more subtle methods yet ere his hand would touch the goal which so tantalisingly eluded him.