The Buried Pyramid

Plucky young Jenny Benet, a recently orphaned American girl who was raised on the Wild West frontier and educated at a Boston finishing school, has come to Egypt in company with her uncle Neville Hawthorne, a prominent British archaeologist. They're part of a team investigating the legendary Buried Pyramid, the tomb of the pharaoh Neferankhotep – who may also have been Moses the Lawgiver.
But they're not the only ones interested in the site. Another party, led by the opulent and treacherous Lady Audrey Cheshire, is shadowing theirs. Someone who signs himself "The Sphinx" has been sending threatening letters – written entirely in hieroglyphics. In Egypt, an ancient and shadowy organization seems determined to keep the tomb from being discovered.
But mortals may not be all that stands in their way.