E. Phillips Oppenheim 
The Evil Shepherd [EPUB ebook] 

A businessman is found stabbed through the heart, the obvious suspect his partner: Oliver Hilditch, a cold-eyed fellow with a paper-thin alibi. Francis Ledsam is a defense barrister and is congratulating himself on a brilliant performance which has just seen Oliver Hilditch acquitted of murder. His ego is pricked by Margaret Hilditch confessing to him that Hilditch was guilty of crimes far more monstrous than murder. Ledsam vows never again to defend a guilty man. But when his newfound principles run up against the harsh reality of real-world justice, he finds himself trapped between his love for a beautiful woman and a powerful desire to do the right thing—no matter the cost.