Sisters of Isis is a book series by Lynne Ewing who is also the author of the popular Daughters of the Moon series and the companion series Sons of the Dark. It is about three girls who live in Washington D.C. who have never met until a priest named Abdel brings them together. They each can cast spells from the Book of Thoth and have the power of transformation. They each have a birthmark in their hair and a ring that the goddess Isis gave them. They are Descendants of Horus. The Sisters have to stop the cult of Anubis from bringing chaos and destruction into the world. If they fail, they will spend eternity with the demons at the edge of chaos.