Sisterhood of Karn

The Sisterhood of Karn was a female society dedicated to protecting the Sacred Flame, which produced the Elixir of Life.

The Sisterhood was a remnant of the Pythia's power. (NA: Cat's Cradle: Time's Crucible)

The Sisterhood entered into the Pact of Rassilon for protection under Gallifrey they also fought against Morbius when he attempted to invade Karn. (PDA: Warmonger)

When the Sacred Flame appeared to be dying, the Sisterhood suspected the Doctor of trying to steal the remaining Elixir, but later helped him defeat Morbius. (DW: The Brain of Morbius)

After Romana became President of Gallifrey, she opened diplomatic relations with the Sisterhood. (NA: Lungbarrow)

They also make a reappearance in the Eight Doctor audio adventures season two two-part finale, Vengeance Of Morbius, trying to prevent his resurrection.