On a winter evening, assorted guests are at their supper in a remote Scottish inn. Suddenly, a brilliant light descends; a spaceship has landed on the moors, and the group are trapped within an invisible wall surrounding the house and garden. The invader is Nyah (Patricia Laffan), a pitiless dominatrix whose powers are demonstrated through a robot under her control. With every Martian male wiped out in a definitive battle of the sexes, she has been sent to Earth to capture suitable breeding stock. As their escape attempts meet with icy contempt, the helpless humans must decide who will die to save the others...and possibly the world!