The film opens at sea, in a storm. A fisherman hauls in an ornate box and after prising it open finds a baby boy and his dead mother. He and his wife raise this child as their own, loving him just as much as their flesh and blood daughter, whom they bear some years later. We know this because Pete Postlethwaite tells us so. This boy, Perseus, does not know it, but he is a demi-god, the son of Zeus himself. And he is about to get caught up in a conflict between humanity and the Gods of Ancient Greece.