The fourth season starts off with everything in transition. Elena faces her worst nightmare as she awakens from her deadly accident to find she must now endure the terrifying change of becoming a vampire — or face certain death. Stefan and Damon are torn even further apart over how to help Elena adjust to a life she never wanted, and everyone must cope with the chaos created after the vampires and their supporters were outed to the town council and local leaders. Despite everything, as Elena and her friends enter into the final stretch of high school before graduation sends them on different paths, they feel the bond to their home town of Mystic Falls take on a deeper meaning when a new mysterious villain is introduced who seems intent on destroying it.
Elena awakens on the morning after the accident to find the thing she dreaded most has come true – she died with vampire blood in her system and now must go through the terrible transition to become a vampire…or face certain death. Stefan promises Elena that he and Bonnie will exhaust every possible way out of the situation, but Damon is furious with his brother for letting Elena die in the first place. Bonnie pays a terrible price for her attempt to change Elena’s fate, while Damon takes out his frustration and rage on Matt. In a rare moment of empathy, Rebekah is deeply touched by Stefan and Elena’s devotion to one another. Finally, Pastor Young and the Town Council members begin rounding up the vampires and their supporters, leading to an unexpected tragedy.
Elena tries to cope with the extreme highs and lows that are part of becoming a vampire, and Stefan and Damon almost come to blows while arguing about what is best for her. Damon decides to help Elena in his own way and asks her not to tell Stefan. A stranger, Connor Jordan, arrives in town and begins questioning Sheriff Forbes and Mayor Lockwood. Connor’s actions quickly convince Stefan that they are dealing with a dangerous vampire hunter. Jeremy and Matt are surprised to see a girl they used to know, April, has returned to town and is enrolling at Mystic Falls High. At a town gathering, Elena comes close to losing control until Caroline steps in to help her. Finally, Damon confides his feelings to an unexpected friend.
Connor continues his search to uncover the secrets of Mystic Falls and tries to convince Jeremy to work with him. With Dr. Fell’s help, Damon and Klaus question Connor, but the confrontation takes a lethal turn. Trying to keep her new life as normal as possible, Elena is determined to continue her senior year at Mystic Falls High with support from Matt and Caroline. Rebekah’s arrival at school makes it difficult for Elena to control her anger, but she learns that confronting Rebekah can be extremely dangerous. Later, Rebekah realizes how alone she is, and reaches out to April. Stefan takes Elena on a thrilling motorcycle ride in an effort to show her that life can still be fun. Tyler gets a surprise visit from Hayley, a werewolf who helped him through the ordeal of breaking his sire-bond to Klaus. Concerned about Elena, as well as his own emotions, Stefan turns to a sympathetic Caroline for advice.
Damon goes with Elena and Bonnie to visit Whitmore College, where Professor Shane is taking over the Occult Studies classes formerly taught by Bonnie’s grandmother. At a fraternity costume party, Damon takes advantage of the wild scene to give Elena a lesson in choosing a victim. Rebekah’s attempt to buy Matt’s forgiveness falls flat, but she is intrigued by unexpected news from Klaus. When Stefan questions Klaus about Connor’s motives, Klaus reveals a long-ago encounter with a powerful group of vampire hunters, but it’s Rebekah who delivers the information that stuns Stefan.
Stefan and Klaus form an uneasy alliance to try and contain the danger that Connor has unleashed on the town. When Connor takes Jeremy, Matt and April hostage at the Grill, Stefan and Damon have a serious disagreement about the best course of action, and Elena is again caught between the two brothers. The situation quickly turns violent when Klaus sends one of his hybrids, Dean to stand up to Connor. Caroline is surprised to find Hayley at the Lockwood mansion. Meanwhile, Professor Shane works with Bonnie to help her get past her fear and guilt.
Terrifying hallucinations leave Elena shaken and confused, causing her to make a dangerous mistake. After giving Stefan some very disturbing news about Elena, Klaus takes matters into his own hands. Professor Shane reveals a story of ancient witchcraft to Damon and Bonnie. With help from Klaus and Stefan, Jeremy begins a new chapter in his life. Finally, Elena makes a painful personal confession to Stefan, and Matt gives Damon startling new information about Professor Shane.
Caroline does her best to be there for Stefan and Elena in a tough time. Damon tries to convince Stefan to help him uncover Prof. Shane’s motives, but Stefan is intent on carrying out a different plan with Klaus. At the annual Miss Mystic Falls Pageant, Elena and Caroline give April advice on which dress to wear, while Tyler and Hayley work together on a secret project, and Damon confronts Prof. Shane with his suspicions. Alarmed by the vivid nightmares he’s having, Jeremy turns to Matt for help, but the situation escalates sooner than anyone expected.
When Stefan confronts Damon with a suspicion about Elena, Damon has no choice but to help Stefan investigate. Searching for answers, Damon and Stefan visit modern day New Orleans to see if they can find anyone who remembers the events of their last visit in 1942, including one of Damon’s former flames, Charlotte. Elena, Caroline and Bonnie share a girls’ night while the Salvatore brothers are out of town, and emotions run high when Elena delivers some shocking news. At Hayley’s urging, Tyler confronts one of Klaus’ hybrids, Kimberly, and the situation quickly escalates into violence. Finally, Damon is faced with a heartbreaking decision.
As a Winter Wonderland-themed party fills the streets of Mystic Falls, Stefan and Caroline find themselves at odds with Tyler over his plans for Klaus and his hybrids. When Caroline proposes a solution to their problem, Hayley finds a dramatic way to make it clear that she is not on board. Later, Klaus makes a discovery that leads to chaos and violence. Meanwhile, Elena and Damon retreat to the Gilbert Lake House to help Jeremy conquer some dangerous inner demons with the help of Bonnie and Professor Shane, who reveals a piece of ancient history that leaves them all speechless.
Appearing unexpectedly at Mystic Falls High, Rebekah wastes no time trying to force Stefan, Elena and Caroline to answer her questions about the search for a cure, leading to a bombshell piece of information from Elena. When Bonnie’s father, Rudy Owens, accepts the role of Interim Mayor, he makes it a priority to protect his daughter, who isn’t at all comfortable with the role he suddenly wants to play in her life. Professor Shane continues to encourage Bonnie to believe in her powers, but he soon finds himself in danger when he reveals too much to the wrong person. Later, Caroline does her best to comfort Tyler after a violent confrontation. Meanwhile, at the lake house, Damon and Matt train Jeremy, trying to raise his game as a hunter, but Klaus is impatient with their progress and intervenes to speed up the process.
Jeremy is furious when Klaus tries to control him by putting Matt’s life in danger. Damon coaches Jeremy as he prepares to take on Klaus’ new vampires, but they find that Kol has beaten them to it. Kol makes it clear that he will stop at nothing to convince everyone to give up the search for the cure. Looking for a new ally, Rebekah reminds Stefan that they were once close friends. When Sheriff Forbes and Mayor Hopkins question Shane about his involvement in the Founders’ Council deaths, Bonnie steps in with questions of her own, and Shane’s responses push Bonnie to the edge of her powers. Elena negotiates with Klaus to keep Jeremy safe, but when danger suddenly appears from a totally unexpected enemy, Elena comes up with her own daring plan for Jeremy.
When Rebekah turns down Klaus’ plea to stop Kol and protect Jeremy, Klaus turns to Stefan for help. After an angry confrontation with her father, Mayor Hopkins, over his unconventional approach to ending the violence in Mystic Falls, Bonnie has a frightening run-in with Kol, followed by an unexpected visitor. Klaus complicates the already tense feelings between Stefan and Damon by revealing a bit of Stefan’s personal life, then surprises Damon by asking for personal advice. Elena tells Stefan about her dangerous plan for Jeremy, leaving Stefan in a difficult spot. When the high school’s 1980s Decade Dance is cancelled by Mayor Hopkins, Stefan finds a charming way to make it up to a disappointed Rebekah.
Shane leads an expedition to a desolate island off the coast of Nova Scotia, where he believes the secret of the cure lies hidden. On the trek to the island’s interior, Rebekah and Elena continue their bitter rivalry, Stefan does his best to keep the peace, and Damon accuses Shane of leading them into a trap. Bonnie and Jeremy try to figure out the message of the Hunter’s mark, while Shane reveals more of the legend of Silas and the witch Qetsiyah, along with his own personal history. Back in Mystic Falls, Tyler confronts Klaus, and Caroline is caught up in the violence that follows.
On the island, Damon has an ugly run-in with a Hunter named Vaughn, and realizes he is one of The Five. Stefan confesses his true feelings about the possibility of becoming human again to Elena. When a stunning new piece of information about the cure is suddenly revealed, it changes the stakes for everyone. Jeremy helps Bonnie recognize what is real and what is an illusion, and Shane is comforted by a woman from his past, Caitlin. Back in Mystic Falls, Caroline and Tyler find that their attempt to translate the code on the Hunter’s Sword is futile without help from Klaus, who has his own reasons for solving the puzzle.
When Stefan arrives back in Mystic Falls with Elena and Jeremy, Caroline is immediately worried about Elena’s state of mind. Stefan reaches out to Dr. Fell and Matt for help. Still on the island, Damon relays somber news to Rebekah, and is surprised at her reaction. Together, Damon and Rebekah learn an unexpected bit of recent history from Vaughn. Everyone is horrified when Bonnie reveals the rest of Shane’s plan. Finally, after Damon does his best to help her, Elena comes up with a plan of her own.
Elena’s new outlook has everyone concerned, leading Stefan and Damon to agree that going back to the normal routine of high school would be the best thing for her. Caroline is pleasantly surprised when Elena decides to rejoin the cheerleading squad, but her pleasure turns to shock when Elena’s behavior proves dangerous. Not giving up on their search for the cure, Damon and Rebekah work together until his unwanted advice catches her off-guard. Klaus tries to use Hayley to get the information he’s after and makes an intriguing discovery in the process. Meanwhile, a bored Elena throws a wild party and gets into an ugly fight.
Realizing that Elena needs some time away from Mystic Falls, Damon takes her to New York City, where he lived and partied hard in the 1970s. When Rebekah also shows up in New York, she’s impressed with Elena’s secret agenda. Flashbacks reveal Damon’s hedonistic life in the underground club scene and a complicated encounter with Lexi. Meanwhile, Caroline and Stefan try to convince Klaus that it would be in his own best interest to help them track Silas down, and Bonnie struggles to keep her grasp on reality and do the right thing.
Elena and Rebekah take off in search of Katherine and find themselves in a small town in Pennsylvania, where Elena has a surprising encounter with another old acquaintance -- Elijah. Stefan and Damon are both concerned about Elena’s state of mind and are determined to do what’s best for her, but she makes it clear that helping her will be difficult. Damon is not sure how to react when Stefan reveals his unexpected plan for the future. Meanwhile, in Mystic Falls, Klaus receives Caroline’s reluctant help and comes to a new understanding of Silas’ powers.
After making a decision that infuriates Klaus, Elijah proposes a life-changing challenge for Rebekah. Caroline finds that her carefully laid plans for the perfect Senior Prom night are disrupted by Elena, so she turns to an amused Klaus for a solution. Determined to get through to Elena, Damon and Stefan both attend the prom, but the evening begins to spiral out of control despite their efforts. When Elena suddenly lashes out in a way no one could have predicted, Matt turns to Rebekah for help. Finally, Bonnie makes a terrifying discovery, and Klaus receives a message that could change everything.
Acting on a mysterious tip that a plot is brewing against him in New Orleans, Klaus makes a trip to the town he and his family helped build. Klaus’ questions lead him to a reunion with his former protégé, Marcel, a charismatic vampire who has total control over the human and supernatural inhabitants of New Orleans. Determined to help his brother find redemption, Elijah follows Klaus and soon learns that Hayley has also come to the French Quarter searching for clues to her family history, and has fallen into the hands of a powerful witch named Sophie. Meanwhile, in Mystic Falls, Damon and Stefan continue with their plan for Elena, while Katherine reveals a surprising vulnerability to Rebekah and asks her to deliver a message.
Damon and Stefan try a brutal new approach to provoke Elena into turning her humanity back on, and Caroline is frustrated when her attempt to intervene backfires. When Elena figures out a way to call the Salvatore brothers' bluff, they call for backup from a surprising source. Matt gives Rebekah some unsolicited advice on her life choices, and she tries to help him in return. Caroline has a confusing and dangerous encounter with Klaus, and Katherine is suspicious when Bonnie makes her an offer that she promises will benefit them both.
As Graduation Day approaches, Caroline tries to distract Elena by focusing on simple tasks like sending out announcements, but Elena won't be swayed from her new obsession. Sheriff Forbes calls Damon and Stefan to the hospital, where someone has been attacking patients. Still trying to force Katherine to help her, Bonnie refuses to give up on her plan to defeat Silas. As a violent wind storm causes a power outage in Mystic Falls, ghosts suddenly appear - some with good intentions and some bent on revenge.
On Graduation Day, Mystic Falls is overrun with ghosts intent on settling old scores and fulfilling their supernatural destinies. Damon’s life is in danger after a ghostly encounter, while Matt and Rebekah join forces to battle a ghost determined to find the cure. As everyone gathers for the graduation ceremony and the ghosts converge, help comes from an unlikely hero. Caroline receives a touching and unexpected graduation present, and Bonnie’s plan leads to the closing of the veil. Elena makes a decision about the Salvatore brothers and faces an epic confrontation with Katherine. Finally, Stefan discovers a horrifying clue to the mystery surrounding Silas.