Orson Scott Card says the following about this book in his acknowledgements: 
 The games with time travel that I play in this book are in deliberate defiance of the consensus rules of science fictional time travel. I decided that I was not going to avoid paradox, I was going to embrace it... 
 Rigg and his friend, Umbo, are on a grand quest. Rigg's father has just passed away, leaving him with a name of his mother (which Rigg never knew) and a bag of jewels. But it's isn't any ordinary quest. The two of them have special talents--Rigg can see the paths of all people, knowing exactly from where they traveled. Umbo is a sort of time traveler, going back and forth between history and present. Put the two together, and they get into all sorts of fun trouble on their way. 
 This story really messes with your mind. It's like what OSC said--take everything you know about time travel and throw it out the window. Umbo first learns that he can travel through time when a future version of himself comes to visit, even though he doesn't yet know how he did it. But that changes the course of time, because now whatever future-Umbo is experiencing won't happen, as he's advised present-Umbo not to do it. The boys are traveling with an innkeeper, Loaf, who acts more like a father than anything else. He and Umbo get into many disagreements over this time-travel talent, which never ceases to be amusing. 
 If you're looking for something to mess with your mind, read this. Despite confusion and paradox it all, somehow, comes together in the end. Or as much as it can... it is a series, after all, so you know the good stuff is yet to come.