The Ape Who Guards the Balance by Elizabeth Peters
Book ten in the Amelia Peabody murder mystery series The prospects for the 1907 archaeological season in Egypt seem fairly dull to Amelia. As a result of Emerson's less-than-diplomatic behaviour they have been demoted to examining only the most boring tombs in the Valley of the Kings - mere leftovers, really. And then, in a seedy section of Cairo, the younger members of the Peabody-Emerson clan purchase a mintcondition papyrus of the famed Book of the Dead, and so begins a new adventure into antiquity. Suddenly, the season for Amelia changes from dull to deadly as she has to untangle a web woven of criminals and cults, stolen treasures and fallen women - all the while under the unblinking eye of a ruthless, remorseless killer.