In the small British town of Dambury, a mysterious military convoy crashes outside the Sunnywise Retirement Home. The vehicles release a toxic substance, which leaks into the local environment and infects the residents of the retirement community. The symptoms of the infection quickly manifest: an overwhelming appetite for raw flesh. They're old, they're angry and they're on the rampage. As the military scrambles to control the outbreak and keep everything out of the media spotlight, a group of regular teenagers find themselves in the thick of the battle against these flesh-eating baby boomers.