Nightrunner (Vol. 2): Stalking Darkness
Alec of Kerry is less than thrilled when the wizard Nysander sends his friend Seregil of Rhiminee off on a mad quest. Seregil is bound by oaths not to tell anyone, even Alec, what is going on. The truth is, though, that Seregil doesn't fully understand the nature of his mad journey himself- he only suspects that it might be related to a previous run-in with dark magic that nearly cost him his life.
I read Luck in the Shadows at the recommendation of a friend, and to be honest I didn't really like it- it felt like it was mainly a setup for this book, with some plot thrown in to make it readable. When I literally tripped over Stalking Darkness, though, I decided to give it a shot, and I am glad I did- it has none of the faults of the prequel, and the writing is so beautiful that I clung to each word. This is one of the rare books in the middle of a series that is by far the best example of the author's work.
While I wouldn't say it is impossible to grasp the overall plot of Stalking Darkness without having read Luck in the Shadows, characters from the first book reappear in the second with little to no introduction.