The Lock — Janet Lovesmith

The lock was huge, rusted, ungainly. It guarded the tomb that lay behind the old house--the tomb of the ill-fated Gantry clan. Lyn Courtney, who had come to work at Gantry Hill, became fascinated, haunted by that lock. Her fears, her hopes, her fantasies centered around it.

Could it explain the puzzling behavior of good-looking Christopher Gantry? The mystery of beautiful, volatile Lila? The invisible creature that even now was stalking young Lyn? She must find out--if it wasn't already too late...