In 1925 Nome, Alaska, winter meant isolation. The cold was unrelenting, and the weather marked by fierce blizzards. The sky was dark. The waters of the Bering Sea were frozen, prohibiting schooners and steamers from reaching the town. The closest train tracks stopped 674 miles away. Horses would die trying to trek across country. Men would, too.

The only source of transportation were dog sleds pulled by hardy Huskies. Teams of mushers carried mail from the railway to Nome, a trip of about a month.

In 1925, this town of 1,400 had lived through the Gold Rush and had settled into a routine of fishing and mining. One doctor, Curtis Welch, served them. Just after the last ship departed for the winter, leaving the town on its own, the first child got sick. He was dead the next morning.

Then another child died, and two more, and another. Highly contagious, with a high mortality rate, diphtheria was spreading throughout the children of Nome. By the next day another child died.

Diptheria can be treated with antitoxin, but although Dr. Welch had stocked many supplies before the last ship left, fresh antitoxin was not among them. The small amount on hand was outdated. Welch sent out an urgent radio signal pleading for antitoxin. Soon after, he received a reply: There was antitoxin in Seattle, and they would fly it to Nome within the week. But planes didn’t fare well in that sort of bitter cold and wind. Many doubted a plane could do it.

Meanwhile, Anchorage also replied. They’d located antitoxin there and proposed shipping it by train to the farthest point, Nenana. But, they asked, could mail drivers and dog teams take the 20-pound package 674 miles from there?

The decision was made: They would pin the hopes of the town on old-fashioned paw power over new-fashioned prop power.

The call to action was immediate. Existing mail drivers were spread out along a relay, with additional ones recruited to fill gaps. One of the additional drivers was Leonhard Seppala, Alaska’s foremost sled dog driver and winner of many races. As the drivers got into place along the trail, Seppala and his team, led by his favorite lead dog, 12-year-old Togo, would continue past all of them to meet a team racing from Nenana with the serum.

It was 50 below zero, cold even for that time of year, and technically colder than it was safe to run dogs. A small crowd waved goodbye as the first team, led by Blackie and driven by Bill Shannon, left the train station and plunged intodarkness. He had 52 miles to cover. But the trail was too jagged, so he had to go out on the frozen river—always risky. Blackie swerved and saved them from a hole in the ice at the last second.

The cold was unrelenting, and the dogs tired. Shannon began to jog by the sled to prevent frostbite. He became hypothermic. His dogs were in bad shape. When he finally made it to the roadhouse six hours later, his face was black with frostbite and several dogs were bleeding from the mouth. It was minus 62 degrees. He still had 22 miles to go. He rested four hours and continued with six dogs, leaving the others behind to be cared for. Children’s lives depended on them.

Meanwhile, Seppala had started on his trek, by far the longest of any: 315 miles to Nulato to meet the serum. He made good time, covering 170 miles in three days. At one point, about 100 miles before the planned relay, he came across another team that had seen a reindeer and had become all entangled in their excitement. He steered his team away, not wanting to be slowed, when the other musher jumped off the sled and ran toward him shouting. Seppala finally made out his words: “The serum! The serum! I have the serum!” The relay drivers had made better time than expected, but Seppala had almost driven past the handoff!

Seppala started back immediately, alarmed by the update the driver had given him: More children had died. The epidemic was spreading even faster. He was faced with a decision: He could take the route that skirted the shoreline of Norton Sound, or he could cut straight across the frozen sound. The former would cost him a day. The latter could cost him his life.

He put his faith in Togo and headed onto the sound. It was pitch black, and the wind was so strong the only thing he could hear were the ice flows groaning and snapping. By the time they reached the other side, the dogs were spent. They had traveled 84 miles in a single day. Behind them, the ice of Norton Sound had already started to break open under the force of 65 mile per hour winds.

After resting, he continued along the shore line, still over frozen ice. But the ice was breaking apart; hours after he traversed it the entire area he’d been on broke off and floated away. Thirteen hours later Seppala reached his relay and passed off the serum. He and his team had traveled 135 miles since picking up the serum, at top speed in blizzard conditions. None of the dogs had been lost, and the serum was on its way.

A total of 20 teams relayed the serum. The next to last team was Gunnar Kaasan, who had been called to help at the last minute. Kaasan worked under Seppala as a musher, so he had his choice of Seppala’s remaining dogs for his team. He chose Balto, a relatively inexperienced dog who was neither very fast nor respected, as his lead dog. By the time the serum was passed to him, the storm had gotten even worse. He was advised to wait. He hit the trail.

Enduring some of the toughest conditions, Kaasan missed a roadhouse where he could have weathered the storm. When he realized it two miles later, he forged on. He couldn’t see anything, and had to rely totally on inexperienced Balto. The wind was so strong he had to struggle to keep the sled on the trail or upright. Finally it flipped. He was thrown in a snow bank. Crawling in the darkness, he found the sled, righted it, and checked to make the serum was still there. It was gone.

Desperately digging in the snow with his bare hands, he finally found it and lashed it to his sled. The trail was better after that, and he arrived at his relay point at about 3 a.m. The next musher was still asleep. It would take time for him to harness his team. Kassan’s dogs were now making good time. He decided to go on.

At 5:30 a.m., February 2, Balto led the team into Nome. Kaasan is said to have staggered up to Balto, mumbled, “Damn fine dog,” and collapsed.

Read more about Balto and Togo:

• Balto the Sled Dog Got a Central Park Statue, but Where’s Togo’s?
• Dogster Hall of Fame: Balto and Togo, Huskies Who Saved an Alaskan Town
• Whatever Happened to Balto, Hero of the Alaskan Serum Run?

About the author: Caroline Coile is the author of 34 dog books, including the top-selling Barron’s Encyclopedia of Dog Breeds. She has written for various publications and is currently a columnist for AKC Family Dog. She shares her home with three naughty Salukis and one Jack Russell Terrier.