In the unforgiving wilderness of Siberia, a group of four Soviet geologists embarks on a perilous expedition to locate a valuable diamond deposit. The team, consisting of the seasoned leader and his dedicated colleagues, sets out with high hopes and scientific determination. As they traverse through the dense taiga and navigate treacherous terrain, they face the relentless challenges posed by the natural environment. Their mission pushes them to their physical and psychological limits, testing their resilience and camaraderie. Amidst the rigorous search, the expedition leader pens a reflective letter, meant to capture his thoughts and experiences, though he struggles to find the right moment to send it.

With the discovery of promising signs, the team's excitement mounts, but their trials are far from over. Nature's brutal elements and unforeseen obstacles threaten their progress at every turn. As they delve deeper into the vast and untamed Siberian landscape, each member of the group must confront their internal struggles and fears. The harsh conditions and isolation amplify tensions, forcing the geologists to confront their vulnerabilities and the stark reality of their predicament. The expedition evolves from a scientific quest into an intense battle for survival, where the endurance of the human spirit is put to the ultimate test.