This is not your father's time travel. There's no machine, there is no dial. There's no telling where or when you'll go. The only thing that can change is you. It will make you what it needs to make you, to fit you in, to make it work. And when you come back, that is if you come back, it won't be the same you at all. You're messing with the nature of things, and the nature of things does not like to be messed with, as Garrett Ronson and his friends find out, the hard way.