The Mysterious Christmas Shell — Eleanor Cameron

When Tom and Jennifer came back to Redwood Cove for the Christmas holidays, something was very wrong. Grandmother seemed fine, Mr. Looper was almost the same, but at the Vinings' nothing was right. The mammoth Christmas tree stood bare of decorations, Aunt Vicky was plainly worried, and Aunt Melissa was even more worried.

Before the first afternoon at Redwood Cove was well started, Tom and Jennifer were involved in the Vinings' problem. Sea Meadows, the expanse of cliff and beach and redwood groves long owned by the Vinings, was to be destroyed. These same hills and meadows where Tom and Jennifer had played, where they had met the Churnadryne, were to be covered by houses and shopping centers--unless they could find a missing will.

When Jennifer finds a beautiful shell on the beach, the clues start unraveling. And when the shell disappears, both Tom and Jennifer as well as Aunt Melissa are in danger of their lives.