The story takes place in the extreme conditions of the Yukon during the 19th-century Klondike Gold Rush, where strong sled dogs were in high demand. After Buck, a domesticated dog, is snatched from a pastoral ranch in California, he is sold into a brutal life as a sled dog. The novella details Buck's struggle to adjust and survive the cruel treatment he receives from humans, other dogs, and nature. He eventually sheds the veneer of civilization altogether and instead relies on primordial instincts and the lessons he has learned to become a respected and feared leader in the wild. The Call of the Wild is London's most popular work and is considered the masterpiece of his so-called "early period". The novella is often classified as children's literature because of its animal protagonist, but the maturity of its subject matter makes it valuable for older audiences as well. Major themes include survival of the fittest, civilization versus nature, and fate versus free will.