7x13 - Buffy the Vampire Slayer

Kennedy, a potential Slayer, takes Willow on a date, which is interrupted when Willow finds herself transformed into Warren. The other Potentials go on a retreat with Giles, who the gang realize may have been replaced by the First. Spike's chip is having agonizing malfunctions, and he and Buffy return to the Initiative to search for a fix.