Kate Humble travels across Iceland to meet the scientists who track the country's most active volcanoes, standing on cooling lava fields and inside monitoring stations where seismographs and gas sensors register the first signs of unrest. She talks with researchers who explain how they read tremors and ground deformation for warning signs before an eruption breaks through the ice caps that cover many of Iceland's volcanic systems. The film also looks back at the country's largest historical eruptions, using their scale to show why Icelandic authorities take even small tremors seriously. Humble's presence keeps the tone conversational rather than technical, following her as she asks the scientists the plain questions about risk and prediction. The result is a portrait of a landscape built by fire, and of the people whose job is to guess what it will do next.