The Aldens try to help a visiting Russian gymnast who is surrounded by mysterious people and events and who seems to have a secret.
Katya, a young gymnast, has come all the way from Russia to stay with the Aldens while she practices for the big competition a week way. The children are happy to share their home with Katya and watch her practice. When someone tries to sabotage Katya's chances of winning, the Aldens know there's a mystery to be solved. But before long they realize that strange happenings aren't limited to the gym: a mysterious figure follows them around the village green, a priceless golden box from Russia shows up in a local pawn shop and, worst of all, Katya seems to have secrets of her own to hide.