Silverthorn
Magician: Apprentice, Magician: Master and Silverthorn are volume one, two and three of the Riftwar saga (I wrongly stated it was the Magician series), with volume four being the last of the saga (there are more series after that). The first two volumes can be read separately from the latter two volumes, judging from the story.
I recently finished reading this book. Quite engaging but I do expect more climatic scenes in volume four. Thankfully there isn't a glaring puzzling thread in this story, unlike the one I spotted in Magician: Master (spoiler). Hope volume four is better!
Comments
From the story, I don't think that's Arutha. It should be Jimmy as he was the only who sneaked into the black building and saw the silverthorn encased in a glass.