Wilkie Collins 
My Lady’s Money [PDF ebook] 

This is a delightful tale of a woman of means who becomes the victim of the theft of a 500 pound note in her home. There are a number of possible suspects and she obtains help in persuing the perpetrator. She retains a young girl as her companion and as she is of much lower rank and may be looked on as the possible thief, she is sent away to her Aunt, Miss Pink, to live until the manner is resolved.
The obstacles in the way of a proper investigation make for a tangled plot. Wilkie Collins gives us a highly original detective too: a dirty old reprobate who does not inspire trust, but is nonetheless awfully good at solving crimes.
And finally there's a suspenseful love story. Two men fall in love with Isabel, and the outcome is doubtful to the very end.