I really don't know if it's possible for me to express how much I love Juliet Marillier. She is one of those fantasy authors whose new books I always read, and I always love them. So this is not going to be the most objective review in the world.
Cybele's Secret is a companion novel to Wildwood Dancing (my review of that book is here), Marillier's first young adult book. The events in Cybele's Secret take place six years after Wildwood Dancing, so I suppose it could be called a sequel, but maybe it is a companion novel because it follows different main characters, and can probably be read as a stand-alone novel. The main character in this book is Paula, the fourth oldest of the five sisters of Piscul Draculai (her sister Jenica, the second daughter, is the main character of the first book). Paula is a scholar, and has joined her father on a trading venture to Istanbul. They are there to procure an ancient religious artifact, one that is both desired and feared. From their first day in Istanbul, they realize that this is a more serious venture than they thought, and already a man has been killed over the transaction. The item in question is Cybele's Gift, an artifact that supposedly holds the last words of the goddess Cybele.
Paula has experience with otherworldly beings from her time in the Otherworld near her home as a child. Her sister Jena had a quest to complete for the denizens of this Otherworld, and her oldest sister Tatiana now resides there with her lover. But Paula never expected to be drawn into a quest of her own. While in Istanbul, she meets three people who will be integral to her being able to finish the quest, two of whom are on quests of their own, and are intricately intwined with her.
One of the things that I think Marillier does best is romance in the fantasy worlds that she creates. But the romance never overshadows the rest of the story. It is essential to the story of the main character, however, and things always look very bleak at some point. But the reader can rely on Marillier to provide a happy ending that fits her characters perfectly. This book, and the one before it, focus more on the quest aspect than many of her other books. Paula must learn and grow to be able to complete her quest. She must remember her strengths and know her weaknesses, and she must be able to trust in love and hope, and friends. Cybele's Secret is a magnificent story, which I liked even better than the award-winning Wildwood Dancing. Readers who enjoy these books should definitely look into Marillier's adult fantasy titles.