Tammy and Greg meet at a party in the Perth hills and sneak away to a disused gravel pit to be alone. They are interrupted by two men burying something who then attack Greg and chase a naked Tammy throughout the night. She is found the next day, delirious and suffering hypothermia. She tells Detective Sam Collins and Jenny Markham what she witnessed and reports Greg's murder. But his body is found in a car wreck, and the crash report says he died because of alcohol and speed on a sharp bend. This casts doubt on Tammy's story and Sam wonders if she imagined the incident. Doubting the official crash report, he and Jenny investigate further and discover two serial killers, who have been burying their victims at the gravel pit, for seventeen years. Sam must lead a huge police task force to try find them before they kill again.