The children form a council to decide how to find treasure. They come up with different ideas, such as digging for buried gold, selling poetry, or becoming detectives.
The children try to sell their poetry to a newspaper editor, but he rejects them. They then decide to look for treasure in an old house, where they meet a mysterious man who claims to be a friend of their father.
The children are kidnapped by a gang of robbers who demand a ransom from their father. They manage to escape with the help of a friendly dog and a boy named Albert.
The children pretend to be Indians and explore the countryside. They encounter a real Indian princess who is in danger from a wicked uncle. They help her escape and return her to her rightful throne.
The children discover a secret passage in their house that leads to a hidden cellar. There they find a stash of wine that they mistake for treasure. They try to sell it but end up causing trouble for themselves and their father.
The children decide to help their father by finding a lost will that could prove his innocence in a lawsuit. An expert in old documents, Albert's uncle was asked to help. They also encounter a rival treasure seeker who tries to stop them.
