Buffy the Vampire Slayer

Buffy's mother continues to be sick and the doctors can't figure out why. Buffy finds a strange orb while on patrol, and later the security guard who pointed it out to her shows up in the hospital apparently crazy. Buffy suspects that there's a supernatural reason behind her mother's illness and goes into a spell-induced trance provided by Willow which reveals Dawn fading in and out of reality.

At the site where she found the orb, Buffy runs into a beaten, captured monk. As she tries to free him she's attacked by an unknown girl with amazing strength. Buffy manages to drag the monk out of the place and get away before the ceiling caves in. He tells her that Dawn is the human form that his brethren made from an energy he calls "The Key". Dawn is not her sister and the memories were all implanted by this group, but Dawn is now human and unaware of her origins.