The Strange Old Man

Timmy sends them a postcard from Russia and tells them about the Strange Old Man. They decide to spy on the old man and discover that he hoards all sorts of things in his small house.
The old man catches them trespassing and scares them away. The girls uncover some puzzling things in the house though and return to discover that his estranged son has been searching for him for years, but an old quarrel has stood in the way of their reconciliation.
The girls decide to help the old man reunite with his son.