The Pauper of Park Lane by William le Queux

Slowly Max Barclay regained possession of his senses. The discovery had so staggered him that, for a few moments, he had stood there in that room, staring at the woman's tweed coat, transfixed in horror.

There was some great and terrible mystery there, and with it Charlie Rolfe, the man whom he had so implicitly trusted, his most intimate friend, and brother of the woman who was all the world to him, was closely associated.