Does anyone remember the title of this book or name of author which I read around the 1060s. Book started with a boy who would eat ants (formic acid deficiency). He was with a mean father or stepfather from whom he escaped. He was able to change his shape. He also had a doll with crystal eyes which turned out to be his power- one was power, the other was a copy. The copies could become free.
I loved this book: got rid of it, got obsessed about it, found it and bought it again, lost it or got rid of it a second time and am again obsessing about it.
Any help around the title would be much appreciated.