Number of pages: 364
In this book, Terry Pratchett provides a time travel story that pays homage (vaguely) to The Terminator (including a very conspicuous reference near the end). The story opens as a standard City Watch novel, as Commander Samuel Vimes is dispatched to arrest a murderer called Carcer, leading to a thrilling chase. However, this unexpectedly ends with a lightning strike that sends both Vimes and Carcer back in time.
In the past, Vimes assumes a new identity after an encounter with the Monks of Time (previously seen in Thief of Time), and joins the Night Watch as a sergeant, where he meets his younger self. However, the young Samuel Vimes isn't exactly cut out to be a member of the watch, so it is up to the older version to train him up. All this time, Vimes is also faced with the prospect of trying to apprehend Carcer and deal with an upcoming revolution.
The opening of this book feels like typical Discworld, with lots of big laughs (the most bizarre moment involves a clock that chimes silences); however, after Vimes is sent back in time, the tone becomes darker and much more serious. There are still laughs, but they are spread a lot more thinly than usual within the book's drama. The story takes advantage of the time travel aspect by including younger versions of Colon and Nobbs, and also features Reg Shoe before he became a zombie; there are a few other self-referential moments that are better appreciated if you are familiar with the Discworld series.
The night watch of this book, are evidently based on the characters of the same name from George R.R. Martin's A Song of Ice and Fire series, and there are some very clever moments, particularly when someone questions if something really is a revolution of the majority of people are rebelling. Overall, I thought this book was enjoyable, though it was difficult going at times, and it felt a bit overlong (it is certainly one of the longer Discworld novels). Overall, it's not a good choice as a first book to read in the series, but it is definitely worth trying if you are a fan.
Next book: A History of Capitalism According to the Jubilee Line (John O'Farrell)