Night Watch by Terry Pratchett

The Time Monks are at it again, in this novel: they've sent Sam Vimes back to the beginning of his career just before the birth of his first child. And Sam realizes that he can't go home until he deals with the criminal who came back with him, lest time be altered too much and his home, family, and career disappear. I thought this book was a time travel story at its best: it pushes the imagination to figure out how all the parts work together, but in the end I was satisfied with how all the parts worked together. I thought the time travel device also worked really well in allowing the series to fill in some great backstory to both the Night Watch and the city's political structure. This book is a great entry in the Discworld series.