It's a sleepy Saturday morning for most people, but not for Iris, who has to feed her many pets before Aunt Mary arrives. Iris likes to call Aunt Mary "Plant Mary" because she is a plant scientist. Today Aunt Mary wants to experiment with making whole wheat sourdough bread from scratch! As the family kitchen transforms into a bread lab, Iris is surprised that bread needs only four ingredients—flour, water, salt, and starter. She also learns about the invisible microbes that make the dough rise, and how flour comes from wheat grown by farmers. It all seems magical, but it's really science.