The Blue Djinn of Babylon (Children of the Lamp #2)

John and Phillipa Gaunt, 12-year-old twins who recently discovered themselves to be descended from a long line of djinn (which are commonly called genies) and who are now in possession of great magical powers, have only just returned from their adventures battling an evil djinn in Cairo and London. Now the mystery surrounding a powerful book of djinn magic lures the twins straight into their next extraordinary adventure.