Buffy the Vampire Slayer Season 3 Episode 12 : Helpless

For her upcoming 18th birthday, Buffy declines the scooby gang's offer of a big party, hoping to celebrate with quiet reflection and a traditional trip to the ice show with her father. But unbeknownst to Buffy, preparations are being made for a life-threatening rite of passage that drains the slayer of her powers and then entraps her with a powerful vampire foe that she must defeat in a defenseless state in order to pass the test.