Sam and Dean investigate a series of missing girls in Limestone, Illinois who all share one thing in common: they are all hardcore Twilight fans. They realize the girls are being preyed upon by vampires in the area and stake out a local bar to find the culprits. While there, the brothers get separated and Dean gets confronted by a vampire named Boris who turns him while Sam seemingly just watches and lets it happen. Afterwards, believing Samuel is going to kill him when he arrives, Dean visits Lisa and Ben to say goodbye but nearly drains Lisa and shoves Ben. When Samuel arrives, he reveals to Dean that as he hasn't drank human blood, there is a cure, but he cannot drink and he must get the blood of Boris for it to work. Dean uses his new senses to track the nest down while a suspicious Samuel confronts Sam as he knows about the cure and Samuel suspects Sam let Dean get turned to get someone on the inside though Sam denies it. At the nest, Boris reveals he wants Dean to be a "recruiter" and that the vampires are building an army under the orders of their "father", the Alpha Vampire. As Boris figures Dean out, the Alpha Vampire sends a telepathic message to all vampires, including Dean, ordering them to continue recruiting. Waking up, Dean is confronted by the entire nest and kills them all single-handedly. Boris confronts him, telling Dean that he has stopped nothing, but Dean kills him anyway. Sam and Samuel track Dean down and cure him, but while reverting to human, he sees that Sam seemingly left him to be turned and becomes suspicious of his brother.
Source: Wikipedia
Source: Wikipedia