Sisters of Death (1977)

⁣FulSix high school girls are involved in initiation ceremonies for their exclusive society, The Sisters.
A shot from a presumably harmless pistol, part of the ritual, kills Liz (Elizabeth Bergen).
Seven years later each of the remaining Sisters receive identical letters inviting them to a reunion in isolated estate mansion.
With nightfall the reign of terror and madness begins as Liz's death is revenged.