In 1947, Thor Heyerdahl, a Norwegian explorer, is determined to prove his theory that the Polynesians migrated from South America to the Pacific Islands, rather than from Asia as widely believed. Despite having no sailing experience and facing skepticism from the scientific community, Heyerdahl assembles a crew of five men. They plan to make the treacherous journey across the Pacific Ocean on a traditional balsa wood raft, aiming to replicate the ancient voyage that could have led to the peopling of Polynesia. The raft, named Kon-Tiki after the Inca sun god, is constructed using only materials and technologies that would have been available to pre-Columbian South American cultures.

The crew embarks from Peru, heading toward the Polynesian islands, over 8,000 kilometers (5,000 miles) away, with only the stars and ocean currents to guide them. Along the way, they face numerous challenges, including unpredictable weather, treacherous sea conditions, and the psychological toll of the vast, open ocean. The men struggle with the isolation and the danger of their journey, but they also experience the immense beauty and power of the sea. Their expedition tests the limits of their endurance and their belief in the theory they set out to prove, pushing them to the edges of human resilience and determination.