Professor Philip Mortimer has decided to spend his holidays in Cairo with his trusty servant, Nasir. There he plans to meet his old friend, Professor Ahmed Rassim Bey, who offers him the fantastic opportunity of satisfying his passion for Egyptology. Professor Bey has invited him to take part in deciphering his latest discoveries—in this case, some papyrus coming from mummies of the Ptolemaic age. Mortimer and Bey soon realize that one of the fragments deals with the "Chamber of Horus," a fabled crypt that could contain priceless treasures...