E. Phillips Oppenheim 
Mr. Marx’s Secret [EPUB ebook] 

Phillip Morton is the son of a yeoman farmer. His mother was a beautiful woman, yet distant. When Phillip was a young boy, his father was pushed off the edge of a slate quarry and fell to his death. A servant from the local castle is suspected, but nothing is proven.
By pure accident ten years later, Phillip meets the lord Ravenor of the local castle. A scholar and adventurer, Ravenor offers to pay for Phillip’s education if Phillip befriends his wayward nephew and provide him a good influence. Along the way, Phillip meets the mysterious Mr. Marx, Lord Ravenor’s secretary. There is something not quite right about Mr. Marx, and it peaks Phillip’s interest.