A grain-drying machine on Andy Barnes's farm in Devon burns through enough diesel to make fossil fuel dependence the episode's starting problem. Eco-engineers Dick Strawbridge and Jem Stansfield arrive with a plan to run the machine on something already piling up around the farm: cow manure. Working alongside Barnes and his three teenage sons, they design and build a biogas plant that captures the methane dung naturally produces and converts it into fuel for the dryer. The film follows the build step by step, from the engineering problems of containing and channeling the gas to the practical work of fitting it into a working farm's daily routine. There's no narration gimmick here, just Strawbridge and Stansfield's usual approach of testing an idea against a real farm's constraints and real deadlines. The episode is less about theory than about whether a family farm can actually replace diesel with its own waste, and what breaks or holds when they try.