The Wife Between Us by Greer Hendricks and Sarah Pekkanen

Meet the ex-wife, the new girlfriend soon-to-be wife and the caring man in their life. The ex-wife is obsessed with her replacement and the replacement is worried about the unstable ex-wife and that she won't be able to live up to her fiance's expectations. They all have secrets. This is another one of those unreliable witness, twisted plot, what-the-heck is really going on thrillers that we latch onto just like the last piece of Halloween candy in the bag. Vanessa is so messed up, Richard is caught between his ex and fiance and Emma is the sweet preschool teacher who has found her Prince Charming - You know nothing (Jon Snow). Don't be fooled by the slow pace of the beginning, this is a race car finish.