The Family Upstairs by Lisa Jewell

Libby Jones has just turned twenty-five.  That's a milestone birthday for anyone but especially for her.  That's the day she reaches the age at which her trust about which she knows nothing is viable.  Along with not knowing anything about the trust, she doesn't know anything about her life before she was adopted at ten months by her parents.  She wonders if she will get all the answers she has been waiting for.

The first surprise is that she has inherited a mansion in one of the most expensive London neighborhoods.  The kind of property that is worth millions.  But that's where the good news stops.  Far from losing her parents in a car accident, she learns that they were suicide victims who left her in a crib while they died.  Apparently, she also has/had siblings about whom nothing is known since that day as they vanished and have never been found.  Were they killed?  There was also another man found dead with her parents and he was never identified.  There were rumors of other adults living in the house along with other children, all with no identity and all never heard from.  Libby has been handed a mystery.

The mystery continues as she attempts to reconcile the stories she has been told with the truth.  While in the house one day, she hears someone upstairs, yet the doors were all locked when she entered.  Is she imagining things?  The truth when she learns it, brings both horror and joy.

This is the second Lisa Jewell novel I've read.  This one was particularly interesting to me with many characters who were relatable.  The mystery unfolds slowly enough that the reader is drawn into the events, imagining how things must have been and slowly realizing the horror that the house was.  This book is recommended for mystery readers.