The Dark Horse by Marcus Sedgwick
Reading level: Ages 9-12
Sig is a boy in a coastal tribe, the Storn, long ago in a northern land. On the day of the wolf hunt, the life of the tribe changes forever, for Sig rescues a small girl, more like the wolves who shelter her than a human. Sigā??s family adopts her. They name her Mouse, and Sig becomes a loyal brother to this girl with disturbing powers and a secret past.
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One day Sig and Mouse find a mysterious box on the beach, and a stranger, a magician, comes in search of itā??and of Mouse. The shocking discovery of Mouseā??s true identity brings to life a terrifying legend and leads to war, betrayal, and Sigā??s coming of age as he struggles to save his tribe.