A troop of Brownie Scouts volunteers to assist with the town's tulip show and becomes drawn into the life of a Dutch family who operate a windmill nursery, including the young girl who befriends them. A persuasive promoter stirs commercial ambitions, and the girls encounter mysteries around a locked house, hidden treasures, a man in gray, and a library window that lead to accusations and misunderstandings. Using resourcefulness, teamwork, and small-town events like a flower show and a garden project, they solve puzzles, protect a secret, and bring about a cheerful resolution.