On a mountainside in Tennessee lies an abandoned quarry, flooded long ago by an underground river. There, in the gathering shadows of a winter twilight, something happened to a nine-year-old girl named Nan Lucas. Something that left her daredevil playmate Tucker Wills, dead and her memory crippled, unable to recall the horror. Twenty years later Nan has returned to Tennessee, but not to remember the past. Now a trendy Manhattan fashion photographer, she comes seeking refuge from the shock of her collapsed marriage. In the old farmhouse inherited from her grandmother, she begins to reorder her priorities - among them, a more solid relationship with her young son, Stephen. Common sense says the imaginary playmate who consumes most of Stephen's time is only a normal invention for a little boy who has no companion his own age. Yet Nan cannot ignore her mounting fears that the mysterious figure Stephen calls "Woody" is both very real and very dangerous. Joining forces with an old mountain woman said to possess the gift of second sight, she struggles to save Stephen from the shadowy companion who seems to be compelling him toward destruction. Yet as hope and time run out, Nan comes to understand she must somehow pierce the veil of her forgotten past and reach into the dark recesses of her memory to rediscover what happened in that long-ago twilight at the quarry when Tucker Wills died.