A lot of this book hurt my head. Time travel does that. I'm always trying to figure out how it works. I usually can figure out if the way they do it breaks the rules, but I'm usually to lazy to think about it hard enough. 
 All in all, I quite liked this book. I liked how there was no romance (yay!) 
 Rigg was arrogant and there were times when I wanted to strangle him. 
 Umbo was fantastic. As was Loaf. As was Param. As was Olivenko. 
 (view spoiler)[Also the twist in the end regarding who Rigg's 'father' really was was brilliant. I mean, an expendable? Awesome. (hide spoiler)]