Importance of Book of Shadows

Along with the Belwicket tools, Morgan has another relic from her birth mother. Morgan finds the Book of Shadows in Selene's library. It's an official diary that her mother kept, but Morgan discovers that Maeve also wrote secret entries, only visible under Maeve's athame. The secret entries tell the story of the man she fell in love with. She cheated on Morgan's father Angus, but Ciaran her had a wife and child. The man was Maeve's soul mate.