Buffy the Vampire Slayer: Season 6, Episode 10
Wrecked (27 Nov. 2001)
When they return home from their nights out, Buffy is ashamed of having slept with Spike and Willow is exhausted from casting spells all night. Amy takes Willow to a sorcerer named Rack whose particular brand of magic quickly has Willow hooked. Later, Willow and Dawn decide to go out for a movie, but Willow's recklessness with magic puts Dawn's life in danger.