Several friends travel to Sweden to study as anthropologists a summer festival that is held every ninety years in the remote hometown of one of them. What begins as a dream vacation in a place where the sun never sets, gradually turns into a dark nightmare as the mysterious inhabitants invite them to participate in their disturbing festive activities.

1402. Queen Margrete I has gathered the Nordic kingdoms in a union, ruled through her adopted son, Erik. But a conspiracy is in the making and Margrete finds herself in an impossible dilemma that could shatter her life's work: The Kalmar Union.