After meeting their neighbors, Hen believes that Matthew, the husband of the two, has something to do with a murder that happened two years ago. A murder that Hen was obsessed with at the time. And the more Hen observes Matthew, the more she starts to suspects him of actually committing the crime. But nobody believes her and think it’s because of her bipolar disorder.
 
After this book I think I know that Peter Swanson is an author I want to read everything from. Swanson is a master in writing fascinating, scarred and twisty characters and always manages to add some unexpected twist in his stories. He did that here too. Hen is an unreliable narrator, because of her mental health issues and the fact that she is on medication. When I know a book features an unreliable narrator, I’m in. It’s one of my favorite thriller tropes. When Hen believes her neighbor Matthew is a murderer, people immediately start doubting her. It’s frustrating for her, but also for you as the reader. Because you’re seeing things through her eyes most of the time and you really want to believe her. But then again, what if she is imagining things? You’re constantly asking yourself that question.
 
“Before She Knew Him” has a great mystery and is fast paced. It has some great twist, but that final twist is one you either love or hate. I found it really satisfying and a lot of it made sense. The book had some moments where it lost its pace a little bit, but overall, I enjoyed this thriller a lot.