A nuclear apocalypse wipes out the human race, turning the earth into a dead planet. Four families survive in Turin, sealed inside an equal number of mini atomic shelters they have dug in their backyards. The surviving families are completely isolated from each other, with a video satellite transmitter their only means of communication. They quickly realise that they do not have enough food to survive. And one of them, Anne, knows she is pregnant. Forced by the outside radiation to stay in the bunkers, what will they do? At a certain point, the inhabitants of one of the shelters begin to hear strange noises, as if someone were "knocking" on the heavy armoured door, trying to get in, even though the TV camera trained on the ground level makes it clear that no one is out there. In just a few hours' time, the strange events become more frequent...