During a sleepover, teenagers Katie Embry and Becca Kotler discuss the urban legend of a cursed videotape that kills whoever watches it after seven days. Katie admits she watched it a week ago. At 10:00 pm, Katie experiences supernatural phenomena and flees to her bedroom, where she is killed by an unseen force. Becca is institutionalized after the experience.
At Katie’s funeral, Rachel, Katie’s aunt and a journalist, is asked by Katie’s mother, Ruth, to investigate the mysterious circumstances behind her daughter’s death. Rachel’s son, Aidan, possesses a sixth sense. Rachel discovers Katie’s boyfriend and two other teenagers all died at the same time. After learning they spent a weekend at Shelter Mountain Inn, Rachel travels there. She finds the videotape and watches it in the cabin where Katie stayed. The video contains haunting, abstract imagery. Afterwards, the cabin’s telephone rings, and a girl’s voice utters “seven days” to Rachel.
Rachel recruits the help of Noah Clay, Aidan’s father and a video analyst. Rachel makes a copy for further study. Rachel discovers hidden footage of a lighthouse on the tape. Her research leads Rachel to identify the woman on the tape: a deceased horse breeder named Anna Morgan, who committed suicide after a strange illness caused her beloved horses to throw themselves off the cliffs of Moesko Island. Rachel discovers Aidan watching the videotape and informs Noah.
Leaving Aidan in Ruth’s care, Rachel heads for Moesko Island to speak with Anna’s widower, Richard Morgan. At the same time, Noah travels to Eola Psychiatric Hospital to view Anna’s medical files during her time there. On the ferry to the island, Rachel spooks a racehorse which escapes its pen and jumps to its death. She discovers Anna had an adopted daughter, Samara, though when speaking with Richard, he denies having a child.
Rachel speaks with the island’s General practitioner, Jane Grasnik, who explains Anna could not conceive, so she adopted Samara. However, Samara possessed an uncontrolled ability called thoughtography and tormented her parents with nightmarish imagery. Noah also learns of Samara’s existence, and heads for the island.