The Finders Keepers Rule: A Maryellen Mystery (American Girl: Beforever)

Maryellen takes a break from practicing for the big "Rock Around the Clock" holiday dance to go to the beach with her friend Davy. While playing in the waves, they find a barnacle-encrusted ring buried in the sand. They imagine that it's lost treasure from a sunken ship. But why do other people seem desperate to get the ring?