His Dark Materials: #1 Northern Lights: Junior Edition by Philip Pullman
When Lyra's friend Roger disappears, she and her daemon, Pantalaimon, set out to find him. They travel to the ice kingdoms of the North, where armoured bears rule and witch-queens fly through frozen skies. Lyra possesses a device that will aid their quest - if she can decipher its mysterious messages. But it knows terrifyig secrets about their journey, and the dangers that await them in worlds far beyond their own