Buffy The Vampire Slayer (1997) - 7x02 - Beneath You

Soon after Buffy's first day as Sunnydale High Guidance Counselor, the gang meets a young woman, Nancy, who's dog was eaten by a large creature living in the sewer. Spike offers his assistance in tracking down the monster, but the gang and Buffy are still a little uneasy with him being around.
The gang soon discover the cause behind the monster is an old, estranged friend; who is relishing in her return to form.
Meanwhile, Willow has mixed emotions as she prepares to leave England and return to Sunnydale.