Lilly's mommy is an architect, and while walking together to her first day of school, she learns that Mommy helped design one of the houses in the neighborhood. Upon arriving at school, Lilly meets a boy with a new baby sister and learns that babies come from mommies and daddies.Lilly begins to wonder about how she was made without a daddy and rushes home after school to find out the answer. Together, Lilly and Mommy explore what it means to be donor-conceived and how generosity and genetics combined to create a home built not just by an architect, but by love.