The Killer is an assassin who was targeting nuns of the Abbey of St. Elspeth Citharede. She was in reality Sister Anna, the supposed first victim (who was actually Isabella, a dancing girl who wanted to join the abbey).
After interviewing Isabella, Sister Anna was seemingly possessed by what she believed was the spirit of Saint Elspeth. She killed Isabella and disguised the body as her own, then dressed in various rags to disguise herself. She killed Sister Elena for her affair with the troubadour Valerio, using a tunnel in the abbey's kitchen to approach and escape. She was caught by Sister Cecilia, who claimed she was the Ripper, the assassin who killed Saint Elspeth. She later killed Sister Catherina, a novice who was dancing with Valerio. While she was committing the murder, she was confronted by the adventurer brought in to instigate the murder and Valerio. She later targeted Sister Cabbage, who turned out to be a dummy set as a trap to catch her. She fled up the clocktower, taking Sister Debora hostage, and declared that she had been chosen by Saint Elspeth to cleanse the unworthy from the abbey. The bell rang and Sister Debora managed to escape, disarming Sister Anna and fleeing. She came to her senses and was then either killed by the player, committed suicide to redeem herself, or tried to fly like an icyene, believing herself forgiven. Regardless, she fell from the tower to her death.