A Promise to Keep — Lois A. Sunagel

Lovely Linda Allen becomes involved in a deal to swap the use of her home for the summer with a woman in New England. Within forty-eight hours after her arrival there, Linda discovers the body of a man in the river that borders the property of her new home. Then two days later she finds the body of a woman in the barn, but the corpse mysteriously disappears when Linda goes for help.