The Ghost in the Garden. Crystal Cove Cozy Ghost Mysteries, #5

Sally O'Brian is delighted when she is asked to help the children at the school where she had taught for most of her career to plant a vegetable garden. The portion of the school yard where the Principal wanted to place the garden was wasted space, a large mud pit that had filled with water after the recent winter rains. She and two friends work out the details of how to drain the water, then fill the pits with extra soil to level the area out.
It's a great plan.until she hears a voice calling to her. "Help me!" cries an ethereal voice that only Sally can hear. Then, as the water level recedes and the mud is scraped away, the eighth graders uncover a human hand. "Get the children back inside, " yells Sally. She certainly can't allow the children to learn that there's a ghost in the garden.