In 523 BC, the Persian pharaoh Cambyses dispatched an army across Egypt's desert to destroy the oracle at Siwa-only for the entire force to be overwhelmed by a sandstorm and lost forever. Two and a half millennia later, a mutilated corpse is washed up on the banks of the Nile at Luxor; an antiques dealer is savagely murdered in Cairo; and a British archaeologist is found dead at an ancient necropolis of Saqqara. The incidents appear unconnected,...