Marley's best friend moved to Chicago. The girl misses her very much, writes letters to her friend and waits for a new meeting. However, instead of an answer, he receives information about a meeting with a lawyer. Marley's classmates - Isla and Sai - also come to the meeting. It seems that Mr. Summerling, an old neighbor, has bequeathed a treasure to the three of them, which the children must find by following the clues left behind.