1997’s Deep Secret is the first of two novels in Diana Wynne Jones’ Magid series.
Through no fault of his own, magid Rupert Venables is drawn into two pressing succession problems. The first problem is to find a magid trainee. The former head magid has died (well, he’s dead but not exactly gone; such is the nature of magids). Rupert is now the senior magid and needs an apprentice and future successor. The second problem is finding the true heir to the Koryfonic Empire, hidden away by the previous, rather paranoid, emperor.
It’s no use asking the emperor himself: Timos IX is very sincerely, very thoroughly dead. So are Timos’ friends and confidants, who might have known where the heir had been stashed. The bomb that reduced Timos IX to vapour was very large.
Rupert decides backburner the question of the missing heir and focus on the quest to find an apprentice and head-magid-to-be. That should at least be straightforward.