Aurora rode Balu, but her eyes never left the creature beside her. Muriel's giant raccoon moved with a grace that seemed strange for such a massive body. Its tail swept the ground, kicking up dust, and its teeth appeared in a low squeak whenever it moved too much on top of the bear.

Intrigued, Aurora took a closer look. She remembered her first night in Tron: several elders arriving on animals that looked like they had come out of a nightmare—or a myth. She remembered the weight of ...