Underground Horror

A year ago, the childless Smith couple from a small town adopted strange children. Two twins (brother and sister) and their one-year-old sister were found in an abandoned sewer collector, which had a reputation among the citizens. Some said there was a cannibal-animal living inside, others spoke of an unknown monster and others still whispered tales about the door to Hell. In any case, the children remembered nothing about themselves and how they had ended up there. For a year they lived happily and cloudlessly until one day the entire family disappeared. The only thing that the baffled police discovered were the footprints of the adults and children leading from the house to the old sewer collector...