I've read way too many YA books that all look the same; there are a ton of red flags that stop me in my tracks (instalove, hot guy who changes the main character in the first five minutes, boring teenagers). Relativity, by Cristin Bishara, dodged pretty much all of them; it started out fresh and smart and kept it up pretty much all the way through.
Start with Ruby, who kicks butt.
She's smart, independent, well-read, and rational. She has a tattoo on her neck and a crush on her best friend, and is incredibly frustrated that she's had to move from LA to Nowhere, Ohio, because her dad got married in a whirlwind romance. And her new stepsister, Kandy, is pretty awful.
Through one thing and another, she finds herself wandering through different universes--places where history has gone very differently than it has for her. Her new family, the loss of her mother when she was young--what does life look like with these factors changed? Or if Thomas Edison didn't invent the light bulb?
I won't say that the science was unassailable; there's definitely some fate stuff happening here. But there's some good science discussion, some nice handwaving bits about how the multiverse might work. More importantly, though, when Ruby has a phenomenon to investigate, she grabs a notebook and a digital camera, goes to the library to do background research, and works hard to figure things out. The girl is THINKING. When she does make less-than-stellar decisions, it's in situations where I don't blame her--stress, panic, and the sheer bewilderment of what she's learning--heck, I wouldn't have done as well as she did.
Anyway, I had a blast with this book. Definitely among the best straight YA I've read in a while.
(Disclaimer: I received a free copy of this book from Netgalley for a review. If you think this is why I'm giving it four stars, you should check out my other ARC reviews. I am not that easy.)