Supernatural (2005)

S6E5 Live Free or Twihard

When a series of young girls vanish, Sam and Dean uncover a vampire coven lurking in a quaint town. During a confrontation with two of the vampires, Dean is bitten and begins to transform into one of them. Samuel informs Dean that the only way to revert his condition is to obtain the blood of the vampire responsible for his transformation. Determined to save himself, Dean goes undercover in the vampire nest, leading him to an unexpected encounter with the Alpha vampire.