This is the sort of science fiction that will satisfy fantasy readers who particularly crave books that take place in pre-industrial societies. The main characters in Pathfinder - young teenagers Rigg and Umbo, plus their adult friend and protector Loaf - have adventures as they journey from village to town, occasionally eating or staying in smoky, atmospheric, dangerous inns. There are magical abilities galore, and even a plot involving a dethroned royal family and a long-lost prince.
But wait - this is Orson Scott Card. Therefore, the reader finds out fairly quickly that the world Rigg and his friends inhabit was colonized more than 11,000 years ago by 19 spaceships from Earth. And those magical abilities? They are all variations of a genetic mutation one of the colonists passed on to his descendants.
And that genetic mutation involves the ability (voluntarily or involuntarily) to manipulate time. Various characters possess different versions of the talent - Rigg can see the paths of all people past and present; Umbo can speed people up (or slow time down), and can also go back in time; and so on.
Card loves to mull over concepts, and so his characters do this quite a bit in Pathfinder, especially concerning the nature of time and paradox. This no doubt interferes with plot momentum (and makes for a VERY long book), but I found it fascinating. Those for whom When You Reach Me by Rebecca Stead provided much fodder for thought will feel the same about Pathfinder.
Card says in an afterword that he purposefully chose a view of time travel that most find paradoxical. Here's an example:
Let's say I eat an egg salad sandwich at a deli. Within hours I am in terrible agony - the mayo or the eggs must have been bad! Luckily, I have the ability to go back in time, so I go back to the moment when I was waiting in line to order and tell myself "don't get the egg salad!"
So - let's go back in time ourselves now. I'm waiting in line at the deli. Suddenly my future self appears, looking haggard and hollow-eyed, and whispers to me urgently "don't get the egg salad!" I'm well aware of my own ability to go back in time and have learned to heed my own warnings. Therefore, I order a cheese sandwich instead.
Here's the question - do I still need to make sure I go back in time to warn myself not to eat the egg salad?
No! Because I've already been warned, and therefore it's in the past. That other future (in which I ate the egg salad, threw up for 4 hours, and then went back in time to warn myself) no longer exists. It's a loop that has been rendered unnecessary and obsolete, so it has ceased to exist.
So there can be no paradoxes, according to Card. You can't go back in time, step on a butterfly, and go back to a totally altered time. If it's that altered, you probably never went back in time at all. You see?
Well, naturally there are a thousand questions and arguments to make, but that's the cool thing about the topic!
For another, lighter view on the subject, here's what Douglas Adams says about time travel in The Hitchhiker's Guide to the Galaxy: