A Coin of Edward VII by Fergus Hume

The Morley family--a husband, his wife and her three children from a former marriage, one young ward, and a governess. Add Giles Ware, a young man who was engaged by a family agreement to the young ward, the fact that hes in love with the governess and you have the start of a mystery. Not long after, the young ward is found dead and the governess has disappeared with a mysterious man. Mr. Ware and a detective, Mr. Steel, search for the governess and unravel the mystery.