Pyramids!

Pyramids; Terry Pratchett (HarperTorch, 2001, ISBN 978-0-06-10265-0; cover artist not known).

Pteppic (or Teppic) has a problem. He's escaped from the trap of being part of a dynasty, has spent years training to be an assassin, and had just passed his final exam with the Assassins Guild in the city of Ankh-Morpork when the call comes to return home. His father, the king, has died. He must take his place on the throne!

Back to Djelibeybi (ignore the "D") he goes where he is caught in endless rituals, a life rigidly controlled by the seemingly ageless Dios, high priest of all high priests. There's a handmaiden, Ptraci (or Traci). Or is she his aunt? And how does a camel get involved in higher mathematics?

Toss in a whole string of restless undead, a dimensional accident, pyramid power, and Death (strangely enough, one of the most popular characters in the series) and you have another fun romp on the back of the turtle.