Pratchett, Terry. Discworld series

Sam Vimes is a man on the run. Yesterday he was a duke, a chief of police and the ambassador to the mysterious fat-rich country of Uberwald. Now he has nothing but his native wit and the gloomy trousers of Uncle Vanya (don't ask). It's snowing. It's freezing. And if he can't make it through the forest to civilisation there's going to be a terrible war. But there are monsters on his trail. They're bright. They're fast. They're werewolves--and they're catching up. Sam Vimes is out of time, out of luck, and already out of breath