Move over, Sherlock Holmes; girl detective Amanda Dagger is on her first case. Using brilliant logic and powerful observation, Amanda sets out to find a friend's scrimshaw medallion, which has mysteriously disappeared. She teams up with Freddy Dash, the class clown and detention pro, and the friends uncover more than they bargain for. Shattered glass, a runaway truck, and a near drowning leave the young sleuths wondering why someone is trying to scare them away from the medallion and from uncovering the truth.

Amanda and Freddy have a common interest in history, which leads them to a notable local landmark, the Old Stone House. Joined by Freddy's tagalong brother Todd and their quirky classmate Brook Winter, the group decides to make it their summer hangout. But strange things seem to be happening on the grounds of the home. Once owned by wealthy ivory merchants, the eerie house has a disturbing past. When Todd is dragged violently underwater while swimming nearby, and a delivery truck nearly collides with the friends, Amanda realizes someone is sending them a message: keep away.

Determined to find the medallion, Amanda and Freddy search the house and discover priceless ivory relics have been stolen. Amanda must learn to trust her instincts to uncover the horrible secrets hidden inside these stone walls and discover what might soon turn a thief into a killer.