Emmy Award-winning and writer-director Nicolas Brown's science documentary is based on American biologist Sean B. Carroll's 2016 book of the same name. It explores how "keystone species" play crucial roles in maintaining the biodiversity of complex ecosystems in the Serengeti, the Aleutian Islands, the Pacific Northwest, and Peru. Its vivid cinematography helps bring to life the work of Bob Paine, Jim Estes, Mary Power, John Terborgh, and Tony Sinclair.