Devil's Dice by William le Queux

My first impulse had been to give information to the German police of Bethune's whereabouts, and thus cause his arrest; yet somehow I could not bring myself to do so. Grindlay and his men would, sooner or later, trace the fugitive; therefore I left the work to them, and returned to London.

As I calmly contemplated the affair in all its phases I became convinced of the strange fact that the mystery surrounding Sybil was the one pivot upon which the whole circumstances revolved. Once I could penetrate the veil, the motive for Sternroyd's murder would, I felt certain, become apparent. But with tantalising contrariness, all my efforts during these dark, anxious days had been absolutely futile. Even though I had, on more than one occasion, to work with the care and caution of a trained detective, I had failed to glean anything further than what my well-beloved had told me herself at the little Pyrenean spa where first she had brought brightness to my life.