There's no doubt that All Our Yesterdays is an exhilarating, exciting read that will have you on the edge of your seat. It took me a while to really get into: there are a few characters I didn't initially like and all the 'secrets' seemed really obvious to me. But as the story went on, I realised that this book achieves a level of complexity rarely seen in YA, and I started enjoying myself a little more.It begins with Em, a girl who's in a prison cell, and her companion Finn, who occupies the next cell. They're observed and interrogated by two mysterious characters, the doctor and the director. Em and Finn are in the future, where everything has gone wrong and the US has become a police state. I liked Em almost instantly, and Finn by proxy because Em thought so well of him the entire time. The more I got to know about them, their struggles for safety and eventual capture, the more I liked them. Em's kick-butt attitude is tempered by her emotional hang ups and reluctance to face her past, and is balanced by Finn's calm nature and ability to think everything through rationally. I like them individually and as a team.We also meet James and Marina, two best friends who live four years in the past, and although I sort of liked James, his dedication to his friends, family and work, I couldn't stand Marina and her friends at all. They are shallow and vain and manipulative, and I simply couldn't make myself sympathise with them. Marina is one of the reasons I started to think about not finishing the book, but I am really glad I stuck it out.In both the past and future, the character development of these four characters is simply amazing. I love how much they learnt and grew, and even Marina ended up redeeming herself. I think this is one the best aspects of All Our Yesterdays - the palpable changes the characters go through because of the events of the narrative. They all find strength in such different ways, some in friends and family, others through emotions or battling their personal demons. Of all of them, Marina struck a chord with me because, in the end, she's just a teenaged girl who incredibly insecure and needs someone to tell her she's fine the way she is.The plot basically races along in All Our Yesterdays, and I found it really hard to put the book down! This is a book where there are no real breaks in the action, and everything keeps snowballing until the climax - I loved it! Although the plot isn't overly complex, one does have to pay attention - it would be easy for a reader to get lost and fail to properly grasp the implications of certain actions and keep track of the possible paradoxes. Everything is well explained though, and I never had any trouble keeping up.I have to note that the basic premise isn't too well grounded in science, and there are a lot of things the author seems to have added to give the scenario a ring of truth, but I guess you have to try a little harder to convince an astrophysicist of your time travel mechanism. I think time travel is one of those things where I'd rather the author used something completely nonsensical like a flux capacitor to drive it, than try to ground it in real science, because I'm going to feel inclined to pick the real science apart. It seems like a particle collider is producing some kind of wormhole, and that scientists have discovered how to magically control which time that wormhole opens up to. It also seemed (to me) like the biggest cop-out to introduce some kind of mystical time-force that essentially freezes events so that time-paradoxes couldn't occur - it allows the author to worm her way out of the biggest challenge in writing a time-travel novel (pun intend).My other complaint is the alarming frequency at which anything girly is given a negative connotation in the book. Marina complains that she's acting like such a girl, Finn says this is going to make me sound like such a girl and one of the characters calls another a slut (which the 'slut' in question embraces, but still). I felt like there was a constant denouncement of anything girly in the background of the whole book, and it disturbs me.I love the way Terrill has written the book from both the past the future points of view, and although it's never any huge secret how they are linked, I still liked not knowing what was going to happen, and guessing, and getting it wrong. I think the memory flashes are a clever device that allow us to glimpse what happened in the four years separating our protagonists without it dragging the action down.I enjoyed All Our Yesterdays a lot and will be recommending it to anyone who wants to read a YA novel with a difference. I think the book brings something fresh to the genre, and fans of science fiction will enjoy it greatly. Although it works perfectly as a stand-alone novel (which I believe it was intended to be), a sequel has been announced. I'm not sure what can be added to the story, but am keen to find out.A copy of this book was provided by the publisher for review.You can read more of my reviews at Speculating on SpecFic.