From the NEW YORK TIMES bestselling author P. B. Kerr comes the fourth volume in this exceptional, imaginative adventure series about a brother and sister who discover they are djinns.Djinn twins John and Philippa are off on another whirlwind adventure that takes them around the globe and into unknown worlds. And it's a race against time as they attempt to rescue their mother from her fate as the Blue Djinn of Babylon. An aging curse has been placed on their father, and if the twins are gone too long, he'll rapidly become an old man. Meanwhile, museums all over the world are reporting robberies of valuable jade from their collections, as well as bizarre hauntings.