The Perfect Nanny by Leila Slimani

 When Miryam had her daughter Mila, she decided to be a stay-at-home mother. Then she had baby Adam. And soon was slowly losing her mind being at home all day with 2 little kids. She decided she wanted to resume her career as a lawyer, so she and her husband Paul set out to find a nanny. They get a recommendation for a woman named Louise, who seems perfect. As time goes by, Louise becomes more and more engrained in the family's life to the point where, when she starts acting a little strange, Miryam isn't quite sure how they can remove her from the family. 

The story starts with a tragic event then explains what led up to it. You feel sorry for Louise, who was left with a mountain of debt after the death of her abusive husband and is barely keeping her head above water. And you feel bad for Miryam, who was an excellent lawyer and really not suited to being a stay at home mom--though others judged her for her decision to return to work, including Paul's (really obnoxious) mother. It's a thought-provoking look at motherhood along with a page-turner of a thriller.

Though the novel is set in Paris, it is loosely based on the true story of a nanny and her 2 charges in New York City.