I am always a bit wary when books are marketed to be for "fans of ..." Especially when it is a book that I didn't care for. I am a fan of this author, but I was concerned I might not like The Ex because I hated The Girl on the Train. If you haven't read either, I would say read this one, not that one. The Ex was really good! It's a very engaging, twisty mystery with likable characters. This book would make a great movie! 
 In The Ex, Olivia is called by her ex-fiancee's daughter to see if she can get him free from jail. He is accused of shooting and killing three people in the park. One of whom happens to be the father of the kid who shot and killed his wife 3 years before. Olivia is convinced that Jack is innocent and will do everything to get him free. But with the evidence staked against him, she has a very steep uphill battle to climb. 
 One thing that I really liked about this book was that it kept me guessing. Until the end, I wasn't sure if Jack did it or not. I'm not going to spoil it for you, so you'll just have to follow the clues along with Olivia. I really liked Olivia's character, She is smart with tons of flaws, but is totally up front and honest about those flaws. I like strong female characters like that. 
 I highly recommend this book. With all of the secrets, twists and surprises, you won't be able to put it down!