After spending the summer enjoying her passionate relationship with Damon, and making sure that Jeremy is adjusting after his return from the dead, Elena is thrilled to move into the dorm at nearby Whitmore College with her new roommate, Caroline. Still believing that Bonnie has been traveling all summer and will soon join them, Elena and Caroline are surprised when a student named Megan shows up and announces that she will be sharing their dorm room. Katherine makes an unexpected appearance at the Salvatore house and pleads with Damon to help her now that she is human and vulnerable to her enemies. Matt and Rebekah return to Mystic Falls after spending a wild summer in Europe, where they met a mysterious beauty named Nadia. Elena can't shake the feeling that something is wrong with Stefan, and Silas makes a terrifying appearance at the "End of Summer" party in the town square.
Without telling Elena that Stefan is missing, Damon turns to Sheriff Forbes for help finding his brother. Elena and Caroline try to find out who is covering up a campus hug, and a fellow Whitmore student named Jesse gives Elena some intriguing information about Professor Wes Maxfield. While Jeremy struggles to return to his old life, he continues to be the only person who can see and talk to Bonnie, but he can't convince her that it's time to let the others know that she sacrificed her own life for his. After learning that Silas is searching for Katherine, Damon asks Matt and Jeremy to keep her out of sight, but the situation quickly spirals out of control. Finally, Nadia uses violence to make a point about her own agenda.
When Elena and Katherine have the same dream that Stefan is in danger and desperately needs their help, they convince Damon to help them find Stefan. However, their plans are thwarted by a mysterious young woman named Tessa who seems to know everything about Stefan's history. In flashbacks to a distant time and place, Tessa reveals the shocking secrets in her past and what she has planned for the future. She also has a disturbing message for Damon about his own future. Silas forces an unwilling accomplice to help him search for Katherine, leading to a confusing and life-threatening situation for Matt. Finally, Silas reveals the reason he's determined to find Katherine, and Damon and Elena face a disturbing new reality.
While Mystic Falls observes its traditional Remembrance Day to honor the dead, Damon and Elena try to help Stefan through a confusing time, a task that ends up taking Elena on an emotional journey of her own. A worried Matt tries to figure out the reason behind his mysterious blackouts, and Caroline makes an effort to get to know Jesse better. Jeremy makes a startling confession that hits Damon hard. Finally, Dr. Maxfield puts a plan in motion that will change everything.
On campus, Elena is touched by a sad and secretive student named Aaron. Elena and Damon attend the Whitmore Historical Ball dressed as Anne Boleyn and Henry VIII. At the Ball, Elena shares a dance with Dr. Maxfield, who has a disturbing message for her. Caroline's evening at the Ball takes her from happiness to heartbreak. Meanwhile, Nadia reveals her surprising history to Katherine, and Damon tries to make a deal with Silas. Silas' demand that Damon commit an unthinkable act leads to a unhappy confrontation.
Silas happily announces his new goal to Damon and Elena, but they are skeptical when he promises to accomplish one important task in return for their help. Tessa confidently tells Stefan about her next move, then realizes that Silas has managed to outsmart her. A desperate Katherine discovers a new and unexpected consequence of becoming human again, and realizes she needs a new place to stay. In exchange for a spot in the dorm room, she offers to show Caroline how to get answers from Dr. Maxfield. Bonnie is touched by Jeremy's strength and determination to stand by her. Finally, Damon is stunned when he figures out the secret to Tessa's plan.
While Elena and Damon try to explain Amara's situation to Stefan, Dr. Wes gives Katherine some deeply disturbing news. Nadia shows up at Caroline's dorm room, searching for Katherine. After a surprising conversation with Amara, Jeremy and Bonnie share a glimmer of hope. Silas fails to keep a promise, causing Damon to turn to Tessa for help with his new plan, and Stefan makes a heartbreaking confession to Damon and Elena.
At Whitmore College, Elena and Caroline decide it's time to throw a big party, but their plans are interrupted when Jesse suddenly needs Caroline's help. At Elena's request, Damon comes up with an effective method to get Wes to answer his questions. At the party, Elena finds that she and Aaron have a lot in common, and Caroline grows more concerned about Jesse. Meanwhile, Katherine does a favor for Matt and manages to get through to Stefan, who is still struggling to overcome the events of the summer. Finally, Bonnie does her best to cope with her new reality, and Damon makes a terrifying discovery about a secret society.
Stefan continues to offer Katherine his support while trying to mask his own pain, until Caroline shows up with an unusual form of therapy. After trying to make amends with Caroline, Elena grows so concerned about Damon that she turns to Aaron for help. Later, when Damon tells Elena about a terrible ordeal in his past that he has kept secret for decades, she shares the disturbing information she just learned about her own family. Finally, Aaron decides on a desperate course of action after a conversation with Dr. Wes.
Damon realizes Elena is in danger and enlists Stefan's help to find her. The brothers pay a visit to Aaron, and Damon shocks Stefan by revealing his first-hand knowledge of Aaron's family. In an attempt to stop Damon, Dr. Wes unleashes his secret weapon, forcing Damon to deal with a part of his past he thought was gone forever, as well as the consequences of his decades-long plan for revenge. Meanwhile, Elena is horrified by Dr. Wes' confessions about the dark history of Whitmore College and his own ultimate goal. Finally, a frantic Katherine turns to Matt for help, until she realizes that Nadia may be the one who can solve her problem.
As she faces a new crisis, Katherine remembers the traumatic night in 1490 when she gave birth to the daughter who was immediately taken from her. Stefan lets Elena, Caroline and Bonnie know that Katherine's health has taken a turn for the worse, while Damon Matt and Jeremy discuss some of Katherine's most notorious moments. Nadia comes up with a frightening plan to protect her mother, and Stefan and Elena are forced to help her. Meanwhile, Caroline is mortified when she realizes she forgot to fill Elena in on the latest shocking gossip, then indulges in a little scandalous behavior of her own. Finally, Elena and Katherine share an unexpected moment of connection.
When Enzo brings Damon a gruesome present and insists that they bond by committing an act of revenge, Damon makes an effort to do the honorable thing. After finding himself in awkward and confusing conversations with Nadia, Matt impulsively decides to throw a party, where Caroline makes a stunning confession to Elena, then has to face the consequence of her actions with Stefan and Tyler. Aaron does his best to make amends for his family's past misdeeds and start a new life for himself. Finally, Elena suddenly finds herself in a life-threatening situation with only minutes to figure out how to save herself.
Hoping to help everyone move past recent traumatic events, Caroline convinces Elena and Bonnie to attend Whitmore College's "Bitter Ball" for broken-hearted students. Bonnie is intrigued with a fellow student named Liv, who appears to be dabbling in witchcraft. Tyler starts to worry about Matt's relationship with Nadia. After making a disturbing discovery, Stefan has a frustrating conversation with Damon and Enzo. Dr. Wes struggles to continue his research project with help from a new benefactor named Sloan. Still bent on revenge, Damon and Enzo resort to violence to convince Bonnie and Jeremy to help them, but their plan takes an unexpected and horrifying turn.
As Damon's behavior escalates from destructive to deadly, Stefan begins to regret their last conversation and decides to track Damon down and intervene. For reasons of her own, Elena volunteers to come along. Dr. Wes enlists the Travelers to set a trap that will once again test Damon's friendship with Enzo. After a heart-to-heart talk with Nadia, Matt enlists Caroline and Tyler's help to protect Elena, leading to a unhappy confrontation. Later, when Stefan tries to comfort a dejected Caroline, their conversation leads to a horrifying realization.
While Nadia remembers her centuries-long search for her mother, Stefan, Caroline and Matt come up with a desperate new plan to save Elena's life. For the second time, Bonnie and Jeremy must turn to Liv for help. Damon baits Tyler into a nasty confrontation, then takes off to seek revenge on Dr. Wes. Caroline and Tyler come to a new understanding. Finally, Bonnie learns of a terrifying secret that will threaten the lives of all her friends.
When Stefan tries to explain recent events to a very sick Elena, her first instinct is to call Damon. At the same time, Damon is trying to figure out how to make a disturbing confession to Elena. While going through Dr. Wes' files, Caroline discovers a frightening secret, and is surprised when Enzo appears, claiming to have the solution everyone is searching for. At Enzo's insistence, Caroline asks Stefan to meet her at a mysterious location where they are joined by a group of Travelers, including Sloan, who reveals new information on the importance of doppelgangers. During spring break on a mostly deserted Whitmore campus, Elena runs into Luke, a student who seems to know her, though she has no memory of meeting him. Recently dumped by his boyfriend, Luke proposes that he and Elena spend the break getting drunk together, but she sends him off on an urgent mission to find Bonnie and the "newbie" witch, Liv. Damon finally tells Elena the truth about his recent activities, and they come to a new agreement about their relationship.
In order to keep Stefan from being harmed by Sloan and the Travelers, Caroline and Enzo agree to make a trip to Atlanta to find a newly discovered doppleganger. Caroline is surprised when Enzo opens up to her about his past. Damon and Elena spend an awkward afternoon at Jeremy's parent-teacher conference, where they hear bad news about his behavior at school. Afterwards, Damon reluctantly tells Elena upsetting news about Jeremy's personal life. Bonnie has an unsettling encounter with Luke, and learns more about his family history. Liv fills Jeremy in on the rumors about the Travelers' next move and demonstrates her considerable power. Jeremy makes an unexpected deal with Liv, then makes a decision that is devastating to Elena. Stefan and Caroline share a special moment of friendship. Finally, a terrifying turn of events at the Travelers' camp leads to the appearance of their mysterious leader, Markos.
Both Stefan and Elena are suddenly having unsettling dreams of an alternate version of the life they might have had together. Bonnie has a disturbing encounter with Grams, who warns her about frightening changes on the Other Side. Enzo gives Damon unwanted relationship advice, then admits he is searching for a woman he loved decades before while he was held captive by the Augustines. Liv enlists Matt, Jeremy and Tyler to help track the Travelers and keep them from taking control of Mystic Falls. Bonnie is hurt and angry when she learns that Jeremy is working with Liv behind her back. Luke shows up at the Salvatore house and explains what he knows about Markos and the Travelers to Damon, Elena and Enzo. Matt has a terrifying encounter with inhabitants of the Other Side. Finally, when Damon finds Markos, he is both relieved and disturbed by what Markos has to tell him.
Stefan tries to distract Elena from obsessing about the state of her relationship with Damon, while Bonnie does her best to be realistic about how the changes happening on the Other Side will affect her existence as the Anchor. Damon demands the Traveler knife, forcing Jeremy and Matt to admit it has gone missing. Through flashbacks to election night, 1960, Enzo reveals to Elena, Stefan and Bonnie that he has learned what happened to his long-lost love, Maggie, and then, with the unwilling help of Liv and Luke, things take an ugly turn. Trying to calm Enzo down, Damon intervenes, but his words cause Enzo to make a desperate and dangerous decision that leads to a unhappy confrontation with Stefan. Finally, Markos enlists Sloan's help in a ritual designed to break an ancient curse against the Travelers. Tyler is forced to play a dangerous part in the ritual, while witnessing the incredible power the Travelers now possess.
When Tyler turns up at the Salvatore house with the news that Markos' plan to break the witches' curse puts Stefan and Elena in imminent danger, Damon suggests they hide out in the remote cabin once owned by Caroline's father. Once there, it becomes obvious to Caroline that Stefan and Elena are keeping a secret, so Damon comes up with a parlor game designed to expose the truth. A ghostly presence at the cabin uses violence and fire to make itself known. Meanwhile, Matt takes charge of Tyler's plan to get information from one of the Travelers, and Bonnie continues to keep the truth about the Other Side from Jeremy, despite warnings from Grams.
When Stefan and Elena escape from Markos' control, only to find themselves stranded in a remote location, Stefan gets philosophical with Elena about her relationship with Damon. After their attempt to protect the dopplegangers goes badly, Liv and Luke come up with a dangerous new strategy. Damon recruits Matt and Jeremy to help him set a trap for Markos, who turns out to have a devastating surprise of his own. Bonnie finally admits to Caroline that she's been keeping the truth about the Other Side from everyone. Finally, while Bonnie searches desperately for a way to stop Markos, Caroline is witness to an unthinkable act of violence by one of the Travelers.
Heartbroken by an unexpected tragedy, Damon is focused on holding himself together, while pushing Bonnie harder than ever to find a way to stop the disintegration of the Other Side. Elena takes matters into her own hands and demands that Liv and Luke help her, but Liv refuses to cooperate until Caroline provides her with some personal motivation. Sheriff Forbes is horrified when Markos uses violence against Tyler/Julian to prove that Mystic Falls is now under the control of the Travelers. With new information from Sheriff Forbes, Damon comes up with a dangerous plan that relies on split-second timing from Jeremy and Matt. Liv's off-hand remark regarding Stefan gets a surprisingly emotional response from Caroline. As conditions on the Other Side worsen, Bonnie takes the opportunity to settle an old score. Finally, Damon's plan causes a massive explosion in Mystic Falls, and everyone is caught up in the confusion, leaving a trail of heroism, sacrifice, relief and despair.