Bennie, Jessie, Violet, and Henry Alden are helping a neighbor remove some slippery stones when they discover a strange inscription. The mystery-solving siblings jump at the chance for another adventure and discover right away that Amanda has a secret of her own. They don't press her to reveal it and instead pursue additional clues. Hoping to find the mysterious gold mentioned on the stone, the busy sleuths unearth even more questions.

Everything seems to be coming together when they overhear conversations that lead the children to believe that Amanda's friends are trying to steal the treasure from her.