Buffy the Vampire Slayer (1997)

S7E13 The Killer in Me

Kennedy, an upcoming Slayer, invites Willow out for a date, but their evening takes a strange turn when Willow unexpectedly morphs into Warren. Meanwhile, the other Potentials embark on a retreat with Giles, leading the group to suspect that he may have been infiltrated by the First. Meanwhile, Spike is experiencing severe issues with his chip, prompting him and Buffy to head back to the Initiative in hopes of finding a solution.