The Mummy Case by Elizabeth Peters

Radcliffe Emerson, the irascible husband of fellow archaeologist and Egyptologist Amelia Peabody, has earned the nickname "Father of Curses" -- and at Mazghunah he demonstrates why. Denied permission to dig at the pyramids of Dahshoor, he and Amelia are resigned to excavating mounds of rubble in the middle of nowhere. And there is nothing in this barren area worthy of their interest -- until an antiquities dealer is murdered in his own shop. A second sighting of a sinister stranger from the crime scene, a mysterious scrap of papyrus, and a missing mummy case have all whetted Amelia's curiosity. But when the Emersons start digging for answers in an ancient tomb, events take a darker and deadlier turn -- and there may be no surviving the very modern terrors their efforts reveal.