The Man of Death by Arthur Gask

"MR. LAROSE, I am being watched," said the small, scholarly-looking man with the high forehead. "I live alone in a lonely house on a lonely shore, and I do not know what it means. I am concerned about what is going to happen next."

Agatha Wandsworth never learnt who her parents were, which, under the circumstances, might perhaps have been considered a good thing, as her father had been a dissolute Norwegian sailor and her mother a disreputable and decidedly coarse young woman who had many times strayed from the paths of virtue and part of whose calling was that of an artist's model.