Ecosystems run on hidden dependencies, and naturalist Chris Packham travels to some of the world's major habitats to trace them out. He builds the film around pairings that sound implausible until he explains them: a termite that depends on a rhino, a lynx that needs a caterpillar somewhere upstream in its food web. Each example works the same way, starting with two species that seem to have nothing to do with each other and ending with the chain of cause and effect that links them, drawing on recent field research to make the connections explicit rather than implied. Packham moves between habitats rather than staying in one location, using each stop to add another link to the same argument: remove one species and the effects move sideways through the system in ways that are not obvious from the outside. The film stays close to specific animals and specific relationships throughout, using them as evidence for a broader claim about biodiversity and interdependence rather than treating nature as scenery.