Bitten is the 4th episode of Season 8.
Sam and Dean investigate a bizarre murder in a college town. Close on the tail of their suspect, they bust into an apartment to find two dead bodies and a laptop cued up to some disturbing video footage. The footage begins with Brian, Mike and Kate hearing about an unusual animal attack in their town and the rest of the story is revealed through their eyes. Sam and Dean become unknowing participants in a unique student film.
Sam and Dean burst into a house near a college and search the place. Sam finds a corpse covered with a sheet, a corpse with no ID, and walls covered in blood. The brothers find a laptop computer with a note on it saying "Play me." The Winchesters play it and a video starts up with the words "This should never have ended this way." come up. A student, Brian Wilcox, is filming footage at a diner...
Brian is at the diner with his friend and roommate Mike Wheeler, debating what Brian should make a movie about. As Mike goofs off with his friend's camera, they spot several girls at a booth nearby and Mike good-naturedly suggests they might take pity on Brian. One of the girls, Kate, comes over and asks if they're filming her. She discusses camera technology with Brian but is clearly attracted to Mike.
Later, Brian is at the house. Kate and Mike are in the next room making love. Once they're done, Kate comes out, awkwardly says hi to Brian, and goes to the kitchen. Brian, Mike, and Kate go back to the diner and Brian and Kate talk cameras. Mike doesn't know anything about cameras but Kate assures Brian that she's teaching her boyfriend about them. The friends film each other talking about what they plan to do in five years. Kate wants to be an environmentalist, a lawyer, or both. Brian wants to work in Hollywood, and Mike plans to set sail to the middle of the ocean and take things easy.
Brian is filming a literature lecture by Professor Ludensky on Lord of the Flies. Kate comes in and confirms that Brian is taping for Mike, who has dozed off again. As they leave, another student, Scott Parker bumps into Brian, knocking his camera to the ground. He runs off and the three friends follow. The police are securing a nearby crime scene where a student, Jacob Carter, was brutally murdered. Sam and Dean, posing as FBI agents, are on the scene. The detective in charge tells them that a neighbor woman reported growling noises and Jacob's screams.
Back at their house, the three friends discuss what they saw and figure that it's a good thing that the FBI is checking out the murder. Mike puts on the song that was playing at the diner when he first met Kate as a gift to her. Brian asks him to come with him to test some new cameras and Mike agrees. Before he goes, he privately tells Kate that he's going because Brian doesn't have any other friends.
Brian and Mike film some footage of the stadium and spot Sam and Dean nearby. They listen in as Sam figures that it's a normal murder but Dean believes that they need to dig deeper. As night falls, Brian and Mike spot Scott and his girlfriend making out behind the bleachers. She slaps Scott and walks away, and Scott spots Mike and Brian and chases after them. The friends split up and Mike records himself as he wanders in the woods. Something attacks him, dragging him off-camera. When Brian finds Mike a little later, he realizes that something has bitten his friend. However, by the time he gets Mike home, the bite mark has healed completely.
The next day, Mike gets a checkup but the doctor can't find anything wrong with him. As he opens a door, Mike inadvertently rips it off its hinges and they realize that he is now super strong. He lifts Kate one-handed into the air and wonders if he's become a superhero.
Brian decides to place cameras throughout the house. When Kate notices, Brian explains that he wants to record Mike's origin story and make a film out of it. As Mike eats, Brian says that he wants to go out and get bitten so that they can both be superheroes. Mike refuses, saying that his friend doesn't want what he has. Brian begs him to do it but Mike refuses.
Later, Mike and Kate are using a bong when Sam and Dean arrive at the door. As they hide, Brian answers the door and the brothers ask him if they know anything about Jacob's murder, or rumors of someone being bitten. Brian denies everything and they leave, and Kate and Mike record the brothers out on the porch as they talk about dealing with another Mayan god. They play the tape back for Brian and they wonder if Mike has become a Mayan deity.
That night, Kate dozes off and Mike goes to the bathroom mirror and admires himself. However, as he films himself he realizes that he is growing fangs and claws. He smashes the mirror and then goes to look at the sleeping Kate for a minute. After stroking her cheek, he goes down to the kitchen and empties the refrigerator, but is still hungry.
Scott and his friends are out patrolling the neighborhood, looking for the killer animal. Scott films himself and spots Mike, who says that he isn't in the mood for Scott's antics. Mike runs off into the woods and Scott chases after him, calling him a coward and saying that he'll go after Kate if Mike won't turn around and fight him. As Scott tries to spot him, Mike transforms and attacks him.
The next morning, Brian wonders if Kate is scared of Michael but she says that his being a superhero is kind of hot. Mike comes in, covered in blood, and his friends stare at him in horror. He takes a shower to wash off the blood and then tells them that he killed Scott. They go over the footage that Mike filmed in the bathroom and see his claws, and Kate tells Brian to turn off the camera.
Brian goes to the park where Scott was killed and watches while Sam and Dean talk to the local detective. He tells the brothers that the same thing killed Scott as Jacob and that it left Scott's partially-eaten heart in the street. Michael goes back and tells his friends what happened, but Mike doesn't remember eating the heart. Kate insists that it was self-defense but Brian points out how unlikely that is and snaps at Mike. Mike shoves him across the room with one hand and then breaks down. When he says that he doesn't know who he is anymore, Kate says that he's hers. Brian insists that they have to call the police and that Mike is risking himself and them. Kate angrily tells him that he doesn't understand because he's never been in love and sets out to get some answers about Mike's condition.
Mike and Kate follow Sam and Dean to the morgue and listen as Sam tells Dean that ten years ago there was a similar murder. However, it didn't take place during the full moon. Once they leave, Kate wants to follow but Mike doesn't see the point. Brian arrives, having tracked his friends' cell phone GPSs. They wonder if he can hack anything and he assures them that he can. They follow the Winchesters to a diner and Brian hacks the security camera. Mike goes in with a hidden camera and sits at the table next to the brothers. The three friends watch and listen as Sam finds an entry about how close descendants of the pureblood can control their change and subsist on animal hearts. The brothers figure that one of the purer werewolves came to town, killed its victim, and then decided to stay.
The three friends return to their house and Mike starts to panic, figuring the 'FBI' is after him. Kate doesn't believe that the Winchesters are FBI and that they'll start by looking for the pureblood. Mike doesn't believe it and goes to his bedroom and Kate goes after him. They argue while Brian goes over the footage of the original attack on Mike. He spots something on the ground and calls to Kate, but she slams the door shut. Brian has no choice but to go out on his own and examine the attack site. He finds a pin on the ground and realizes that it's the same one that Ludensky was wearing at his last lecture. Brian goes to Ludensky's office and tells him that he knows what the professor really is.
Later, Brian comes home and finds Kate packing. As Mike comes out, Brian says that he took care of things and they ask what he did. He shows them footage of his confronting Ludensky and asking the professor to bite him as well. He warns the professor that he hid cameras in his office in advance and is transmitting the video to his laptop at home. Ludensky denies being a werewolf until Brian threatens him with a silver blade. Then he breaks down and explains that after the one murder ten years ago, he only ate animal hearts. However, he saw Jacob, weak and alone, and couldn't resist. Ludensky figured that hunters would come eventually so he needed a patsy. He chose Mike since he's always sleeping in and the professor figured that no one would miss him. Brian says that he wants to become a werewolf and forces the professor to bite his arm.
As the footage ends, Brian starts to transform and shows him footage of the office after he left. Sam and Dean come in and attack Ludensky, eventually killing him. With his dying breath, the professor thanks them. The brothers find the camera and take it down, cutting the transmission, and Brian figures that they're safe. He tells Kate that he protected her when Mike couldn't, but Mike figures the Winchesters will trace the feed back to Brian. Brian, angry and disgusted, tells Mike that he's tired of living in his shadow and that he finally has what he wants. Mike tries to persuade his friend that he doesn't want the horror inside of him, the horror that he experienced when he went out of control and killed Scott. Brian tells Kate that she needs him and grabs her, and Mike transforms and attacks him. The two students struggle and Brian stabs Mike with the silver dagger, killing him. Kate goes to her lover, who says with his dying breath that he loves her.
Kate tries to stab Brian, who easily grabs her and says that she'll understand... and then bites her. She locks herself in the bathroom and films herself using a camera, and then goes berserk. Kate finally gets control of herself and calls to Brian, saying that she understands. She goes outside and tells Brian that she understands...and then rips his throat out. Afterward, she covers Mike's corpse with a sheet and then sits down at the computer to record her message to the Winchesters. She tells that she and her friends weren't monsters and didn't want what happened to them. Kate then says that she's leaving and that she will eat animal hearts and never hurt anyone, and promises that they won't hear about her. Before signing off, Kate asks the Winchesters to give her a chance.
Sam and Dean look at the computer and wonder what to do next. Sam hesitantly suggests that they let her leave. Much to his surprise, Dean agrees, saying that they should give Kate a chance. They can always kill her if she fails to keep her promise. They collect all of the evidence that werewolves were there and leave.
Outside of town, Kate hitches a ride to the border and then walks away along the railroad tracks.