It was more than 40 degrees Fahrenheit below zero when Helen Thayer woke up. It was the second day of her journey to the North Pole. She melted ice into water and mixed it with granola, powdered milk, coconut flakes, raisins, and butter. This was her first breakfast of the expedition, and it had to be eaten quickly. The steaming food would freeze in less than a minute.

Thayer looked out at the endless white ice pack that lay ahead of her. She was to spend the next four weeks on the ice, traveling to the magnetic North Pole and back. She would go there on foot, pulling her supplies behind her on a sled, with only her dog Charlie, a black husky, as a companion. Charlie would alert her if she were unlucky enough to encounter any polar bears—a serious threat in the Arctic.

After breakfast Thayer began packing her things for the day’s trip. First she melted ice to fill two bottles of water and mixed in some sport-drink mix. It was important to keep plenty of water and high-energy foods available. The dry Arctic air held little moisture, and Thayer could become dehydrated quickly. Dehydration would make it difficult to keep warm and cause her to get tired faster. Thayer packed the water and snacks, including extra crackers for Charlie, in an insulated bag.

As Thayer began packing her tent, she heard a low, rumbling growl. Charlie had spotted a mother polar bear and her two cubs in the distance. Thayer took a deep breath. Polar bears were always dangerous, but a mother bear that believed she needed to protect her cubs would be even more aggressive. Thayer tried to remember what the Inuit bear hunter had told her about polar bears. “Keep eye contact,” the man had said. “Move sideways or slowly forward—never backward. Stay calm. Don’t show fear. Don’t shoot unless you absolutely have to.” Wounding a polar bear would only incite it more. A wounded bear, especially a mother bear, would be more aggressive. Above all the Inuit hunter had stressed, “Never, ever run.”

Earlier, Thayer had leashed Charlie to a hook that she had driven into the ice. Now she hooked the snarling dog onto the sled, close to her. He was at the end of the leash, gnashing his teeth and growling angrily. The mother bear, however, was not impressed. She kept plodding forward.

“Stay calm. Stay calm,” Thayer told herself. Despite the ramifications of shooting a polar bear, she grabbed her rifle and flare gun from the sled. Thayer loved animals. She didn’t want to shoot the bear, but she might not have a choice. She decided to try a warning shot.

Aiming to the left, Thayer squeezed the trigger. The rifle sent out a sharp, booming report, but the sound had no effect on the bear. It lumbered forward, now only 100 feet away. Thayer fought the impulse to run. She aimed the flare gun to the right and fired. The flaming canister landed a few feet to the side of the bear. The animal glanced briefly at the flare but did not stop.

Charlie strained against the leash, snapping and snarling, saliva flying from his mouth. The bear reared up suddenly and looked at Charlie. Thayer took aim and landed another flare directly in front of the bear. The huge white creature looked back at her cubs. Finally she changed direction, moving off slowly, circling Thayer and Charlie in a wide arc. Twice the bear stopped and looked back, but Thayer shot more flares, and the animal kept going. At last the bear and her cubs disappeared from sight. Charlie’s snarls became a low growl. Thayer gave him a big hug that he scarcely seemed to notice—he was still on guard. She quickly packed the tent. She didn’t want to be around if the polar bear decided to return. She fed Charlie a few crackers and a peanut butter cup. They had passed their first test together on the Arctic ice.