This short film explains the idea of a Trophic Cascade – essentially a process that occurs when predators in a food web lower the number or alter the behaviour of their prey, which in turn has an effect on the the next lower tropic level. This ‘cascades’ down the food web and can have an enormous impact on the many habitats and ecosystems in a particular area. Here, the film looks at the impact wolves had on Yellowstone National Park when they were reintroduced after 70 years of absence. It does appear to portray the wolf as a miracle worker, and overlooks the great cleansing forest fires that took place in 1988. Nevertheless, it illustrates why these decisions regarding species introduction or re-introduction are so consequential and must not be used irrationally.