In 2013, author Lucinda Riley embarked on an ambitious quest: to write seven interwoven novels about seven adopted sisters. Each book would feature one sister, and each sister would set off on her own quest to learn about her heritage. All seven books would include dual timelines and multiple settings from around the world, and there also would be “a hidden plot running throughout like a delicate thread,” as Riley explained it. Moreover, the sisters would be allegorical figures based on the legends of the Seven Sisters of the Pleiades star cluster.