So, this was cute but it was a lot more juvenile than I was expecting. It feels more like it's aimed at middle schoolers even though the protagonist is 16. Which, there's nothing wrong with that, it's just not what I was really expecting. 
 Gwen felt really immature. And for basically the whole book she was a really reactionary character. I know that's how it was supposed to be set up--she's not supposed to know about the time traveling thing--but it didn't really improve until most of the way through the book. Things happened to Gwen, and again, I know that was sort of the whole theme here, but it sort of got aggravating. Especially because all the other characters play the "I know something you don't know" game. And that really infuriates me. 
 Look, it's cool, I like a good mystery. I can enjoy not knowing everything and waiting to be surprised. But it has to feel like you're giving me something to go on. Some clues. And more than total incomprehensible excerpts from some "secret writings" that then get info dumped on us in the following chapter. It never felt authentic. It never felt like I was meant to be catching on to what was happening. Like Gwen, things were just happening to me as a reader and I was meant to go along with it. That really bugs me. 
 The end of this got mildly interesting for me again. There was the right balance of acting and intrigue, I think. It was enough to make me a tiny bit curious for the sequel, Sapphire Blue, which is more than I can say for the other 80% of the book. I'm not really invested in the characters at all (and ugh, a little insta-love, no thanks) but given that I probably read this in about 4 hours, tops, I think I could probably stand to give the rest of this a go. 
 Maybe. Not a high priority, though.