A group of early humans has been lured to the eastern extremes of the North American continent 15,000 years ago. As they settle in their new home, the demands of the once benevolent spirit become more ominous. Too late, their shaman realizes its true nature. The clan is scattered and most are killed when the group tries to resist the demon's will. In the present day, a young engineer and outdoorsman, David Locke, who has spent much of his youth at a family cabin in the Green Mountains of Vermont is familiar with local tribal lore because of his long acquaintance with an old man of Native American descent who lives nearby. Soon after being miraculously spared from certain death in an auto accident, David becomes romantically involved with a young woman, Lori Martin, who he meets during a Sunday outing. However, tragedy begins to strike all around him as close friends and business rivals die. It finally becomes apparent to him that he has become the object of the attention from a supernatural force that is jealously possessive. After Lori is nearly killed, David attempts to convince her that something is wrong. Lori is skeptical and becomes concerned for his emotional state. When he disappears while on a SCUBA excursion, it seems he has been lost forever.

Tom Cairns is a young father living in a suburb in upstate New York. Out one Saturday morning, he is in an automobile accident, experiencing the physical shock of the collision and suddenly finding himself undergoing a near death experience. His transition into another plane is winderous, and he is told that he can stay in an inviting afterlife, or return since it is not truly his time. Hearing his wife call out for him over the distance, he decides to return. After recovering, he is intrigued by his experience in spite of attempts by some to explain away his experience. However, at a sporting event, he witnesses the death by heart attack of a spectator, and is astonished to see the victim's soul separate from his body. The soul is confused but comes to realize that Tom can see him. He sees a passageway open in the distance, and the soul along with a guiding spirit disappear through it. Now fully enthralled, he seeks out others who have had a near death experience and survived. Soon after, however, he realizes that he is being stalked by an malevolent presence. He begins work with hospice patients and finds that he is able to provide comfort and guidance at the moment of passing until an experience with a hardened, defiant drug dealer leaves him shaken as the dealer's soul is dragged away into the dark. The same malevolent being he sensed before remains, menacing him, making Tom acutely aware of its presence, dark nature .... and its intent.