As a tunnel construction project threatens the natural order of one of Japan's last untouched regions, an old man and his granddaughter Haruna's humble lifestyle begins to influence the outlook of a man from Tokyo.

A case-hardened cop is pitted against a young eco-terrorist. The title "island" is an artificial construct in Tokyo Bay, a mountain of garbage, a by-product of Japan’s economic boom years. The film’s protagonist Alan works there, almost buried under society’s detritus; his growing obsession with the search for “what has been lost” turns him into a "dangerous" activist. He targets the industrialist Wada, whose chemical factory secretly discharges toxic waste into the environment. But the cop Terayama, who thought he’d seen it all, starts researching eco-activism and soon suspects the haunted, taciturn young man he’s encountered in the neighborhood.