Winter of the Ice Wizard — Mary Pope Osborne

Merlin the magician and Morgan le Fay have mysteriously disappeared! To find them, Jack and Annie journey with their friends Teddy and Kathleen to a frozen kingdom of ice and snow. There they must go on a mission for the one-eyed Ice Wizard. Chased by wolves and braving terrible storm they have only two things to help them -- a magic rope and the Ice Wizard's strange rhyme:

Take my sleigh
And find your way
To the house of the Norns
In the curve of the bay.
Pay them whatever
They tell you to pay.
Then bring back my eye
By break of day.