The daughters were Marguerite (married to King Louis IX of France), Eleanor (married to King Henry III of England), Sanchia (married to King Richard of Germany, aka the Earl of Cornwall and Henry III's brother), and Beatrice (married to King Charles of Sicily, aka Charles of Anjou and Louis IX's brother).
The book is described by the reviewer as "a beautifully written history book that reads like a modern-day adventure novel. Reading about the lives of these four sisters, their husbands and their families is fascinating. ... Nancy Goldstone has written an intelligent book about an intriguing family of sisters who shaped the destiny of Europe."
Goldstone is also co-author with her husband Lawrence, of Out of the Flames, the story of Michael Servetus, scientist and author of The Christianismi Restituto, book declared heretical and which cost him his life in 1553; and of The Friar and the Cipher, a book about the Voynich Manuscript, which still has not been deciphered.