Julek and Franek are on their way to holiday when the family receives new that Grandpa Leon had an accident. They immediately arrive at an old, neglected manor house where their cousins - Pola and Maria - are already there. Grandpa fells terrible, but he releases himself from the hospital at his own request. He ask his grandchildren for help, but emphasizes that their parents cannot find out anything. His request is a dangerous and unlikely mission, on the success of which his grandfather's health depends. The matter is difficult because the cousins are not on the best of terms, and the success of the plan requires close cooperation. Will the children be able to save their grandfather from an accindent?
—G