When eleven-year-old Theodosia and her cat, Isis, travel to Egypt to return the Orb of Ra and the Emerald Tablet, she hopes to learn more about her origins but finds, instead, the Serpents of Chaos and a precious treasure that suddenly appears and disappears.

Eleven-year-old Theodosia's ability to detect black magic raises her suspicions about a magician known as the Great Awi Bubu, while Henry, home for the spring holidays, discovers an artifact at the Museum of Legends and Antiquities that is coveted by every black-cloaked occultist in London.