Devil's Dice by William le Queux

As the cheerless morning wore on, I sat after breakfast gloomily smoking, trying to verify my first impression that Sybil had been the victim of foul play in the hope of dispelling it. But it was, on the contrary, deepened.

Either I was wrong to think thus; and at any price I was determined to convince myself by facts that I was wrong, or I was right. The sole resource henceforth remaining to me for the preservation of my self-respect and the unburdening of my conscience was ardent and ceaseless search after certainty.