Unnatural Selection (Buffy the Vampire Slayer)

Willow's babysitting job is transformed into a nightmare when her infant human charge is replaced by an evil changeling, and Buffy and her friends must unravel the link between the tiny interloper and some mysterious artifacts uncovered at a nearby construction site.Willow's babysitting job turns nightmarish when the baby is replaced by an evil changeling, and Buffy must unravel the link between the tiny interloper and some artifacts found at a nearby construction site