Lily and her sister are ready to start their first year of college. They move into a beautiful home together, and while exploring her new space, Lily comes upon a sparkly blue mushroom. Since Lily loves mushrooms, she pulls the giant thing from the ground, leaving a huge hole behind. When she peers into the hole, though, her trouble begins.

Lily falls and tumbles down, down, and further down until she lands in a strange, unfamiliar world. She is shocked to see that everything in this mysterious land is made of ... mushrooms. Her adventure has just begun. She makes friends with a spa employee named Amanita. Celeste—a kind, older woman—offers Lily guidance and wisdom.

However, not everyone in Mushroom Land is friendly and helpful. On the contrary, Death Cap is an evil man with secrets. Lily's curiosity has led her to this strange world, but unforeseen challenges wait, including the challenge of how she will make her way home.