The Red Room by William le Queux

I confess to having been half-inclined, when I returned home that night, to take Mabel into my confidence. But I hesitated, because I knew that her frankness and sense of justice would lead her to suggest that I should go to New Scotland Yard and lay the whole facts before the Criminal Investigation Department.

I had no secrets from her -- I loved her far too well. But in this crooked affair I had most foolishly given my word of honour to say nothing.