Dangerous curiosity

It is 1864 and Lizzie Martin leaves London for the coast of southern England to become the companion of Lucy Craven, a teenage girl who lives in seclusion with her aunts and who has recently lost her young daughter. On the way, Lizzie meets Dr Lefebre, who is heading in the same direction. It soon becomes clear that Lefebre is a psychiatrist hired by the relatives of young Lucy to find out if the young woman is insane. Lucy Craven does not believe that her daughter has died, but is firmly convinced that her child has been stolen. The situation is getting more complicated. Lizzie hears voices outside late at night, the landlord appears, whose demeanor seems uncannily familiar to Lucy, and even if he shows up, that the young woman is a bit moody, he's definitely not crazy. The tension reaches its peak when a man is found stabbed to death in the garden.
So now Lizzie has no choice but to enlist the help of her beloved, Inspector Benjamin Ross...