J. S. Fletcher 
Middle of Things 

A wealthy man named Ashton is found murdered in an alley, apparently robbed for his jewellery and pocketbook. The police believe they have the killer, a young man who the next morning tries to pawn one of the stolen rings. Viner, however, the man who discovered the body and who is friends with the accused, believes otherwise. It is a quick race to find the real guilty party in order to save an innocent man. But none of the information is completely clear; the victim has a mysterious past and there is no rational motive. His charge, a young girl named Miss Wickham, proves to be of little help and Ashton had no close friendships. It is up to the lawyers and Viner to unravel the mystery that has roots in royalty. (Goodreads)