Quick-take: Interesting, though complicated.
Jen starts day 0 seeing a horrible crime being committed. She then immediately starts experiencing backwards day-by-day time travel as she tries to unravel and prevent what just happened. This mystery is not a "whodunit" but a "whydunit" becaused we witnessed it on day 0.
The ramifications and paradoxes of experiencing life backwards are interesting. Jen only starts exploiting them as the story progresses, and I think it actually helps she figures out the tricks later. The big one was "Since tomorrow never happens, what I do today does not matter." She then starts to skip work and brazenly break social norms to find out more information about the crime she is investigating.
My main complaint is just how complicated the story is. There are so many names, events, conversations, etc. Then Jen travels backwards in time and now that event suddenly had not occured yet. The conversion had not taken place yet. It gets confusing.
There are 2 pieces that save this book and story. A revealing conversion will happen and then after time traveling backwards... that conversation never happened. Jen can now confront the other character again with a distinct advantage. She already knows all the answers, and she can tell the person is lying. She is just now trying to figure out how deep the lie goes and what to pursue next.
The other part that really helps this book: Jen is constantly summarizing for us. She can't keep notes because those notes will be gone when she goes back in time again. Therefore, she instead summarizes what she knows in her head from time to time. I thought this was a clever idea by the author and I am very grateful for her to keep doing it on a regular basis. I'd be very lost otherwise.
Score: 5/5. This book has a Time Traveler's Wife vibe to it, but TTW is a much better book. Still, if you completed that book and enjoyed it and would like something similar, this book is good. Plus, like I mentioned frequently in my reviews, I really appreciate books that are standalone complete stories. My preferred genre, fantasy, are always trying to kick off a new endless series. Complete story + trying something new + interesting = 5 stars.