The Perfect Nanny by Leila Slimani

I struggled a bit with the plot of this book, which is that the nanny kills the two children in her care.  I am not giving anything away--the book opens with this grizzly event being discovered by the parents, and then the book goes back in time to before the nanny was hired and then throughout her time with the family.
The book is loosely based on an event in late 2012, when news broke around the world that a nanny on the Upper West Side of Manhattan was accused of fatally stabbing two young children in her care. As the children bled in the bathtub, reports said, the nanny—who was so close with her well-to-do employers that they had earlier that year spent several days visiting her relatives—slashed her own throat.  She survived, and has pleaded not guilty to killing the children. To most parents, the headlines were a chilling reminder of the vulnerability of children and the potential for cruelty that their adult caregivers are capable of.
There is so much material here to work with, all of it richly explored.  There is the dependency on the nanny that many have experienced.  There is the loneliness and the emotions associated with the job.  There is the invasion of privacy that is a one way street--the nanny knows all but reveals little.  There is the power differential.  And so much more.  I did not end up with sympathy for the nanny so much as a glimpse of how such a horror could come to occur.  Well written.