I’m wavering between 4 & 5 stars. Time travel is a hard sell for me, too many paradoxes. While the solution was simple & not delved into too deeply in this book, it worked for me. Plus, it’s only a theory the main trio came up with, so if it doesn’t pan out (time is sentient?) the author can toss it & come up with another. MC Em is interesting & shows character growth when compared to her younger self. She ultimately disappointed me with her hesitancy to kill ONE person to save the world. Finn had my heart pretty quickly & I like that he has secrets. The doctor, in all his times & ages, creeped me out. Overall, a hit with me. I was turning pages like crazy. Could’ve done with a bit more killing. Highly recommended.