The ruins of the old castle are a favorite place for children to play - besides the computer, of course. Jon, Tina and her younger brother Peter visit the place every day and also become friends with the occasional resident there. But strange things are happening in the premises of the crumbling castle. Curiosity does not give peace to children. It turns out that the castle is full of secrets, strange things start happening and many people no longer know for sure what is true and what is not... The children slowly begin to reveal what it is really about, and a mysterious boy comes to their aid...