2x03 Bloodlust

The brothers investigate a series of decapitations and cattle mutilations in Red Lodge, Montana, and find that the last victim was a vampire. They then run into vampire hunter Gordon Walker (Sterling K. Brown), who Ellen warns is dangerous. Sam is later captured by a group of vampires, and their leader Lenore (Amber Benson) reveals to him that they have reformed, feeding only on cattle. After being released unharmed, Sam tries, to no avail, to convince his brother that the vampires should be left alone. However, when they arrive at the vampire's hideout, they find that Gordon has already captured Lenore. They try to convince Gordon not to kill her, but he cuts Sam's arm to tempt the vampire. When Lenore resists the temptation, the brothers overpower him. As Dean ties Gordon up, Sam takes Lenore to safety. Dean later admits to Sam that he was wrong about the vampires.