Your grandmother is going to be looking after you since your parents are going away. You have not seen her since you were a small child, but you are told she'll be wearing a purple and yellow outfit. You arrive at the train station, awaiting your grandmother on the platform - but just as you head towards her, another old woman identical to the one on the platform. If you go on the one on the platform and go home, she will reveal herself as this hideous alien imposter as it has a plan to take over the world and you got to come up with a plan to stop her and find your real grandma. One bad ending has her zapping you with a mind-control ray only for you to show her where your mother's rose garden is. She then unearths some alien eggs, to which they all hatch, and she prepares to go conquer the world as you are presumably devoured by the newborn aliens.
When assuming her human disguise, Granny takes on the appearance as your grandmother. She has can be seen wearing a distinctive purple and yellow outfit. She has small glasses and grey/white hair. But her real form reveals her as a green alien with three red eyes. In HorrorTown, her design consists of having on a red jacket, blue dress and an red Victorian bonnet. In some early concept art for her design in HorrorTown, she is shown to have almost the exact same look as her look on the book's cover.