This third book in the tale of Urza the Planeswalker is much better than the second, Planeswalker, and possibly even better than the excellent The Brothers' War. Picking up where PLANESWALKER ended, TIMESTREAMS tells of the continuing war between Urza and the minions of Phyrexia. Similar to the previous two books, this one spans around 50 years of time, skipping multi-year periods in which armies are built and characters grow older, resulting in a action-packed and exciting read. J. Robert King is a very talented writer, bringing the world of Dominaria to life like few (if any) other MTG authors have.
Most of this book is taken up by battle sequence after battle sequence, with Urza's armies of students and artifacts fighting off a never-ending stream of attacking Phyrexian mutants. While there is action galore, this book also introduces some great and intriguing characters. Jhoira, Teferi, and Barrin are Urza's disciples and proteges and are each developed into believable and highly individual characters that you'll really get to know as the story progresses. Karn, a silver golem that appears in a number of other MTG books (Rath and Storm, Mercadian Masques, and others), is created by Urza in the first chapter, and much of the book is devoted to developing his personality and purpose. The idea of Urza's Legacy, including Karn and the Weatherlight, is also developed here.
Perhaps the most intriguing thing about this book is the exploration of time rifts, where the flow of time is either faster or slower than normal. King does an excellent job of making this concept seem somewhat believable and uses the rifts masterfully to make this story one you're not likely to forget. I'd feel comfortable saying that this is the best MTG book I've ever read.