If New York City that early summer had not begun to seem like a foretaste of Hell, none of it would have happened. I would not have answered the ad in the Village Voice. And, therefore, later on I would not have stood on the shore of a wind-roughened Maine lake, with a man I had never seen before tongue-lasing me for things I had never done. And still later, I would not have found myself in that desolate place three thousand miles away…
So begins the story of Catherine Mayhew, and office temporary and aspiring but unsuccessful actress. Hired by Eunice and Brain Andexter, a middle-aged sister and brother, and by their friend Dale Carling, Catherine accompanies the trio to a large, secluded house in Maine. Her purpose there, the Andexters have told her, will be to bring happiness into the last weeks of their very ill aunt Josephine Andexter. The aged woman has never ceased to grieve over the disappearance of her granddaughter Karen, eight years before. Carefully coached by the Andexters, Catherine is to impersonate the vanished Karen.
The elderly woman accepts her joyfully. But Catherine soon begins to wonder if her employers have other motives besides the one they have declared to her. She is also puzzled by the hostility of Joel Cartwright, who at twenty was the eighteen-year-old Karen's lover. And more and more Catherine wonders about the woman she is impersonating. What was it that sent Karen fleeing from her luxurious home? Why couldn't the private detective find any trace of her? Why did she write the grandmother she had loved a hate-filled letter? What had become of Karen?
After two mysterious deaths and a near-fatal attack upon her own life, Catherine and Joel try to find the answers by following the trail of “the other Karen” -- the real one.