An Eye for an Eye by William le Queux

Together we stood on the lawn near the river-bank gossiping, and as I looked into Eva's flawless face, whereon the expression had now become softened, I longed to tell her the most sacred secret of my heart. Had she, I wondered, recognised in me the man she encountered in St. James's Park when on that mysterious errand of hers? What could have been the nature of that errand? Whom did she go there to meet?

One fact was at that moment to me more curious than all others, namely, her friendship with Mrs. Blain, the woman who, according to the landlord, rented that house of mystery. By the exercise of care and discretion, I might, I told myself, learn something which would perhaps lead, if not to the solution of the enigma, then to some clue upon which the police might work. But to accomplish this I should be compelled to exercise the most extreme caution, for both mother and daughter were evidently acute to detect any attempt to gain their secret, while it seemed more than probable that Eva herself -- if actually aware of the affair, which was, of course, not quite certain -- had some motive in keeping all knowledge of it concealed.