|Starts in Calumet City, Illinois
At a bar & grill, a waitress, Jane Peterson, is on the phone talking to her sister Olivia about the date that she had, and wonders if her date will call. She insists that she wants the truth from him. As she goes about her job, everyone starts telling the truth to Jane. One woman says she ran over a homeless man, another one calls her sad and pathetic. As everyone around her says the truth, Jane takes a gun out of a drawer. She calls Olivia, but Olivia tells her the truth about how she's pathetic, and tells her to call herself.
Dean calls Bobby and tells him what happened with Sam. Bobby agrees that it's a problem, but says that they have to proceed carefully and find out what it is that may have taken over Sam. He agrees to do the research, and tells Dean to work with Sam until he has something. Sam comes over and tells him about a story on a fourth reported suicide out of nowhere. They head out to investigate.
Posing as FBI agents, Sam and Dean talk to Olivia, who claims that she tried to cheer Jane up. However, Sam realizes that she's lying and bluntly demands to know what she really did to Jane. Olivia finally admits that something forced her to tell Jane to kill herself, and she couldn't stop. Outside, the brothers wonder what made Olivia talk in the first place.
A dentist, Paul Conley, is working on a patient who nervously admits that he doesn't want to be there. Paul suggests that they have dinner, and the patient says that his wife is old and ugly, and that he had sex with Paul's daughter, Melissa. Paul angrily grabs the patient and starts drilling into his mouth as blood flies everywhere.
Dean calls Bobby to see if he's found out what Sam is, and insists he can't stand being around him. Bobby warns that it may just be Sam. Dean gives him a day to find out anything more, or he'll handle it himself. Once he hangs up, Dean tries to call Lisa, but Sam comes in and tells him about the death at the dentist's office. He's eager to go investigate, but Dean says that he wants to stay at the motel and do some research. Sam is surprised but agrees.
Later, Sam calls Dean to tell him that Paul committed suicide in his prison cell, and that he killed his victim after the victim told him some unpleasant truths. Sam suggests that Dean check out the dentist's office while he checks out the morgue. Dean closes down his files on doppelgangers and goes to the dentist office. Searching, he finds a bill for saxophone repairs and realizes that Jane played the tuba. He goes to the store and talks to the clerk, who claims to know nothing. However, as Dean leaves, he mentioned a one-in-a-million horn that was stolen from him, and that is over a thousand years old. It was stolen two weeks ago, the same time that Jane died.
At the motel, Dean researches ancient horns belonging to angels, including Gabriel's Horn of Truth, and calls out to Castiel. Castiel appears and Dean wonders why he didn't come when Dean needed him for Sam. The angel admits that he didn't come because he doesn't know anything about Sam. However, he is sure that it isn't Lucifer. Dean wonders why he is no longer acting remotely human, and Castiel explains that he's at war, and certain regrettable things are required of him. When Dean mentions Gabriel's horn, Castiel teleports away, searches everywhere, and returns to tell Dean it isn't the horn. As Dean turns away, angry, Castiel offers to do what he can to find out what is going on with Sam and then teleports away.
At the morgue, Sam asks the coroner if he can see the bodies of the other suicides. The coroner says that they were taken away, and finally admits that they disappeared from their drawers.
Dean is at a bar drinking when Sam calls him with a lead. One of the victims, Corey, died a week before everyone else, in an apparent car crash. Sam goes to the first victim's home and Dean says that he'll meet Sam there. Before he goes, Dean asks the bartender for a drink and admits that he'd like the truth. The bartender then blurts out the truth about her marriage and her drug habit, and Dean realizes what's going on.
As he goes, Dean calls Bobby and discovers that he's talking about how he likes Tori Spelling and pedicures. When Bobby wonders why he's telling Dean that, he admits that Dean is his favorite but Sam is a better hunter. Dean explains that he's been cursed to have everyone he talks to tell the truth, and gets an idea. He calls Sam but gets his voice mail, and says that he's on the way and tells him to call back.
Sam talks to Corey's roommate, who breaks into tears when Sam expresses his suspicions. She explains that Corey thought her boyfriend was cheating on her, and she became obsessed with finding out the truth.
As Dean arrives at Corey's apartment, Lisa calls and falls under the curse. She insists on talking about how Dean shoved Ben, and tells him that he pushes down all of his issues and drinks to suppress it. Lisa admits that she knew she lost Dean the minute that Sam came back, and Dean will never be happy as long as his brother is in his life. She then wonders why she spoke so harshly, and Dean tells her that it's not her fault. He admits that he and Sam have issues, and Lisa says that she and Ben can't be involved with Dean. She hangs up and Dean stares at the phone in despair.
As Sam searches Corey's room, he finds a hope chest with her pet cat's skull in it. He shows it to Dean, who wants to talk. Dean explains about the curse and asks Sam why he stood there and let the vampire attack him. Sam says that he froze out of shock, and he feels terrible. Dean accepts what he's saying and apologizes, and Sam assures him that he has his back and always will.
Back at the motel, Sam explains that the cat skull served as a focus for Corey to cast a spell to invoke Veritas, the Goddess of Truth. Now, everyone in town who asks for truth receives it, in heels. Veritas has a weakness to dogs, and she sought the attention of the masses. Dean realizes that the 21st century version of a Goddess speaking truth would be... an investigative reporter. Sam and Dean do some research on the local reporter, Ashley Frank, and steal her rehearsal videos. They find one scene where a dog barks at her during an on-the-street broadcast. They zoom in and confirm that her eyes are glowing.
That night, Sam and Dean follow Ashley as she goes to her apartment. Dean has knives and Sam provides dog's blood to cover the blades. The brothers go in and find a number of cats, and a shrine to Veritas. Finally they locate the partially-consumed bodies of the suicides. She smashes them unconscious with a wave of her hands.
When they wake up, they're tied to posts. While Veritas pulls the tongue out of one of her victims, Sam uses a hidden knife to start cutting himself free. She admits that she can't wait to eat their tongues, since she treasures the tongues of liars. She compels Dean to tell the truth and asks him about Sam, and Dean says that Sam is just acting like he does himself. Dean says that what he's good at is slicing throats, and he's not a family man and never will be.
Veritas then asks Sam how feels about them getting back together, and he insists that they watch out for each other. Meanwhile, Veritas realizes that Sam can resist her spell, but doesn't know how he's doing it. She accuses Sam of not being human, much to Dean's surprise. Sam frees himself and tosses his knife to Dean, and then attacks Veritas. She starts choking Sam, but Dean grabs the weapon and stabs her, buying Sam enough time to stab her with the tainted knife. Dean grabs another knife and suspiciously confronts.
Sam admits that he lied to Dean, and he's known that there's something wrong with him. He insists that he knew Dean could handle becoming a vampire and finding the cure. When Dean says he could have killed Ben, Sam admits that he's a better hunter, but he can't feel any emotions. Sam says that he needs help. Dean considers it and then puts down the knife... and leaps on Sam and beats him unconscious.