This novella explores life following a devastating plague that wipes out most of humanity.

An early science-fiction story set in 2073, sixty years after a devastating plague wipes out most of the planet's population. One of the few survivors recounts the story of life before and during the plague to his grand-children who have problems believing any of the tale.

The story opens with Buck, a large and powerful St. Bernard-Scotch Shepherd, living happily in California's Santa Clara Valley as the pampered pet of rich Judge Miller and his family. However, he is stolen by the gardener's assistant, Manuel, and sold to finance his gambling addiction. He is shipped to Seattle. Put in a crate, he is starved and ill-treated. When released, he attacks his overseer, known only as of the "man in the red sweater" but this man teaches the "law of the club", hitting Buck until he is sufficiently cowed (but the man shows some kindness after Buck stops). Buck is then sold to a pair of French-Canadian dispatchers from the Canadian government, Fran ois and Perrault, who take him with them to the Klondike region of Canada. There, they train him as a sled dog. From his teammates, he quickly learns to survive cold winter nights and the pack society. A rivalry develops between Buck and the vicious, quarrelsome lead dog, Spitz. Buck eventually beats Spitz in a fight. Spitz is killed by the pack after his defeat by Buck, and Buck eventually becomes the leader of the team.

When Francois and Perrault reach Dawson with their dispatches and are given new orders from the Canadian government, the team is then sold to a "Scottish half-breed" man, who is also working the mail service. The dogs must carry heavy loads to the mining areas, and the journeys they make are tiresome and long. One of the team, a morose husky named Dave, becomes sick and is eventually shot