In 1973, five men and six women drifted across the Atlantic on a raft as part of a scientific experiment exploring the origins of violence and sexual attraction. Nobody expected what ultimately took place on that 3-month journey. Through archive material and a reunion of the surviving members of the expedition, this film tells the hidden story of the project.

Set in the 1970s, Blackwater tells the story of how four random people's lives converge after two tourists are found murdered in a tent near the Swedish mountain town of Blackwater.