Louisa May Alcott 
The Mysterious Key And What It Opened [EPUB ebook] 

The story begins with the mysterious death of Sir Richard Trevlyn. All the reader knows is that Richard’s wife, Alice, who is pregnant with their first child, listens through a keyhole in the library door to a conversation Richard has with a visitor. What she hears horrifies her, she faints, and a servant, Hester, finds her and helps her to bed. Alice insists Richard not be disturbed, but Hester is worried and goes to the library anyway to tell him his wife is ill. She finds him slumped over his desk, dead.

Twelve years later the child, Lillian, meets a stranger on the grounds, a sixteen year old boy named Paul who applies for work on the estate. He does his job well, advancing in position and earning the affection of family and servants alike. Some of the servants suspect he may be more than a mere gardener or groom, but they like him and when he leaves without a word to anyone they are confused and disappointed.