From the top of the world, Hudson Bay looks like an enormous paw print on the torso of the continent, and through a vast network of lakes and rivers, this bay connects to oceans across the globe. Here, at the heart of everything, walks Nanurjuk, or Nanu, one polar bear among the six thousand that traverse the 1.23 million square kilometers of ice and snow covering the bay. From author and geographer James Raffan comes a story about a polar bear's...