Detective Lyolka and the Pencil Gang

"The children's detective story by Olga Popova about Lyolka and the 'Pencil Gang' is an exciting tale of how a girl, through her attentiveness, resourcefulness, and ingenuity, managed to decode a cipher and expose a whole gang of criminals who... were stealing paintings from museums.
Lyolka is an energetic girl who dreams of becoming a real detective. Her dream begins to come true when she and her parents move. On the very first day in the new place, she encounters strange things: mysterious notes, odd pencils, and signs on the fence... She needs to figure it all out. Lyolka takes on the case. To understand what is happening, she has to solve a real cipher! And when the message is decoded, the most difficult part begins - she must catch the criminals.