Finished A Simple Favor by Darcey Bell. I received a copy for review.
Stephanie and Emily are best friends. So when Emily asks Stephanie to watch her son (Nicky) for a few hours, Stephanie agrees. And then Emily never comes back.
This has been compared to Gone Girl but the more apt comparison is to VC Andrews. This book is insane, and your tolerance for that is probably best gauged by your fondness for VC Andrews.
The reviews are mixed. I enjoyed this novel (probably way more than I should have) but there are at least two twists more than there needed to be and those twists are really, REALLY choreographed. But it will certainly hold your interest.