Guardian of the Horizon
This adventure of the Emerson family was written out of chronological order in order to fill in a gap left in the story of Nefret and the Lost Oasis. It takes place in the year 1907 - 1908.
When the Emersons are summoned to come to the aid of their good friend, Tarek, King of the Kingdom of the Hidden Mountain, they do not hesitate to return to Sudan to come to his aid, though they are suspicious of the messenger.
When they arrive, they soon find that their suspicions were warrranted. Tarek has been usurped by one who has no right to claim the throne. The usurper plans to use Nefret and the Emersons to solidify his position.
I've been reading the Amelia Peabody books in order, and was thrown off a bit at first by the out-of-synch chronology. I was soon caught up in the story, though, so that quickly ceased to be a problem, and I quite enjoyed it.