The ghost tree / M.R.C. Kasasian.

"1914: Sixteen-year-old Etterly, running from something, hides inside the trunk of a tree and disappears. The police search but find no trace. Her family and friends wrack their brains, but come up with nothing. And so slowly life returns to normal. The hole in the tree is boarded up and the village of Sackwater moves on. Only Etterly's best friend, Betty, clings to hope, insisting she can hear her friend calling for help. 1940: A skeleton is discovered buried in the woods. Though most clues have long since decayed, it is wearing the necklace Etterly had on the day she went missing. Long haunted by her friend's fate, Detective Betty Church is determined to solve the case once and for all."--Publisher.