Annál az esténél folytatjuk, ahol az előző évad abba maradt. Elenat sokkolja az, ami otthon fogadja: rátalál John Gilbertre és Jeremyre. A kórházban Forbes seriffet Matt, Bonnie és Damon vigasztalja, amíg hírt kapnak Caroline állapotáról. Egy zavaros beszélgetés után Elenaval, Damon az első, aki rájön, hogy Katherine visszatért. Ez összefogásra készeteti a testvéreket, akik megpróbálnak együttes erővel rájönni a nő visszatérésének okára és arra mennyi veszélyt jelent ez szeretteikre. Ezalatt Tylert, aki próbálja feldolgozni apja halálát, elbűvölő és titokzatos nagybátyja, Mason Lockwood látogatja meg.

Mikor a zavart és kétségbeesett Caroline végre elhagyja a kórházat, hogy csatlakozzon barátaihoz a mystic falls-i karneválra, Damon azonnal cselekedni akar, ám Stefan és Elena Caroline védelmére kelnek. Mattet teljesen összezavarja Caroline viselkedése, de még mindig próbálja neki bevallani mit érez. Damonnak gyanússá válik Mason Lockwood, és Tyler hirtelen haragú természetét használja fel a nagybácsi titkának feltárására. A történtek miatt dühös Bonnie pedig Damonon éli ki haragját.

Elena, Damon és Alaric elmennek a Duke Egyetemre, hogy Isobel kutatási anyagai között próbáljanak választ találni a Lockwood család körüli rejtélyes eseményekre. Amikor az erdei tónál rendeznek összejövetelt a fiatalok, Stefan döbbenetes dolognak lesz szemtanúja Masonnel kapcsolatban, és Tyler is gyanítani kezdi, hogy Mason nem mindenben az, akinek mondja magát.

Stefan elhatározza, hogy keményebb eszközökhöz nyúl, hogy kiszedje Katből, miért is jött vissza a lány Mystic Falls-ba. A vallatás során megdöbbentő mozzanatokkal szembesül az 1864-es vámpírirtással kapcsolatban. Damon, aki már tudja, hogy Mason vérfarkassá változott a holdtöltekor, egyedi praktikákkal próbálja meg kiiktatni őt, de azzal kell szembesülnie, hogy Mason erősebb és agyafúrtabb, mint hitte.

A történelmi társaság jótékonysági napján Mason Lockwood elárulja Forbes seriffnek, hogy Damon és Stefan Salvatore vámpírok, és sikerül is őket csapdába csalni. Forbes seriff azonban nem csak róluk szerez tudomást. Eközben Tyler elmondja Jeremynek, hogyan válhat vérfarkassá.

Despite Elena’s efforts to keep Jeremy safe, he offers to help Damon and Alaric deal with Katherine... Sheriff Forbes and Caroline share a few rare moments of quality mother/daughter time. Bonnie accidentally discovers new information about Mason and shares it with Stefan, leading Damon to take matters into his own hands.

Stefan and Damon decide on a new plan to deal with Katherine at the Lockwood’s masquerade ball. Katherine calls on an old friend, Lucy, to attend the ball with her. Bonnie, Jeremy and Alaric all do what they can to help Stefan and Damon, but Katherine has a surprise planned that none of them could foresee. Things take an ugly turn when Matt and Tyler start doing shots with their friends.

An Ancient Presence In Mystic Falls, Stefan and Damon come to Elena’s assistance and, in the process, learn surprising new information about people, vampires and events in the distant past. Jeremy helps Bonnie after she casts a difficult and exhausting spell, and Caroline does what she can to make things easier for Tyler. Finally, Stefan and Damon reach a new understanding.

Elena puts herself in a dangerous position as she searches for the truth about Katherine’s past and what her own future may hold. Knowing that Stefan would never agree to her plan, Elena swears Caroline to secrecy. Damon uses a new-found confidant to help him try to discover the real purpose and power of the moonstone. Jeremy and Bonnie meet Luka, a new student with a surprising family history.

Elena decides to take matters into her own hands and offers a tempting incentive to Rose for her help. When things take an unexpected turn, however, Rose calls on Damon to deal with the plan Elena has set in motion. Jeremy’s reckless attempt to help Bonnie retrieve the moonstone lands him in a life-threatening position and forces Stefan to put himself in danger. Bonnie and Luka form a closer connection. Tyler shows Caroline the Lockwood cellar, where she makes a discovery that leaves them both terrified.

As the full moon approaches, Caroline helps Tyler prepare for the transformation he is powerless to stop. While Stefan and Katherine play mind games on one another, Damon and Alaric are suspicious when a stranger named Jules shows up in Mystic Falls, searching for her missing friend, Mason. Elena is frustrated at the lengths Jeremy and her friends have gone to in order to keep her safe. Bonnie and Luca work together on a spell, while still keeping secrets from one another. Finally, Elijah makes an unexpected appearance with an offer that could change everything.

Stefan has his own ideas about Elena’s new plan for the future. While Damon tries to get the truth out of Jules, he asks Elena to keep an eye on Rose, a situation that turns unexpectedly dangerous. Caroline and Matt try to be honest about their feelings for one another, and Tyler’s reaction to Caroline’s generosity comes as a surprise to her... Damon struggles to hide his true feelings when a life-and-death crisis hits him harder than he expected.

Johnathan Gilbert’s return to Mystic Falls comes as an unhappy surprise to Elena, Jenna and Damon. Caroline lets Stefan know about her conversation with Tyler, and Stefan does his best to reach out to a confused and conflicted Tyler. Jeremy comforts Bonnie after her disturbing conversation with Jonas... When Jules takes a hostage, the situation quickly escalates into a violent confrontation.

Stefan and Elena get away for what they hope will be a romantic weekend at the Gilbert family lake house, not realizing that they’ve been followed. Jenna starts to worry that Alaric isn’t being honest with her. Jules explains the importance of the sun and moon curse to Tyler, but leaves out an important detail. Damon attends a tea at the Historical Society in order to talk to Elijah, but Elijah isn’t giving up any secrets. With help from Caroline and Jeremy, Bonnie uses deceptive measures to get shocking new information out of Luka. Finally, Tyler offers Matt some relationship advice.

Stefan tells Elena about a dark time in his history and the surprising person whose influence changed everything. After getting the truth out of Luka, Jonas makes his feelings clear to Bonnie and Jeremy. Trying to catch Elijah off-guard, Damon arranges a dinner party for him with Jenna, Alaric and Andie, but last-minute information throws Damon’s plan into chaos.

Katherine’s mind games are getting on everyone’s nerves, but Damon, Stefan and Elena realize that her knowledge of Mystic Falls history will help them stay alive. Frustrated with her relationship with Matt, Caroline finds a new way to get his attention. Alaric makes a surprising confession to Jenna, and Katherine makes a different kind of confession to Damon. Stefan and Bonnie try to convince Jonas and Luka that they should all be working together, but Jonas’ lack of trust leads to a violent and fiery confrontation.

Elena and Alaric both lash out at John when Isobel’s unexpected arrival leaves Jenna devastated. Bonnie works with Damon and Jeremy to find the spell they’ll need to harness her ancestors’ power. A heartbroken Caroline doesn’t know what to do about Matt. Stefan and Damon realize they have a new secret weapon.

As the high school prepares to throw a “1960s Decade Dance,” Elena starts receiving disturbing messages from Klaus via an unusual source. Bonnie tries to reassure Jeremy that she is strong enough to help Elena, but a worried Jeremy asks Stefan for advice. Caroline talks Matt into taking her to the dance. Expecting Klaus to show up at the dance, Damon and Alaric attend as chaperones, but Klaus is playing a complicated game that keeps them on edge. Finally, Damon comes up with a new plan of action that shocks and upsets everyone.

Stefan and Damon are furious when they discover that Elena has defied them both to make a new ally and take control of the plan to out-maneuver Klaus. Disagreement over how to protect Elena leads to growing tension between the Salvatore brothers. Meanwhile, Stefan has his hands full trying to keep a confused and frightened Jenna safe. Flashbacks to 1491 reveal Katherine’s introduction to Elijah and Klaus, along with the origin of the moonstone curse. Elena learns shocking new information about Klaus’ motives.

With the arrival of the full moon, Elena tries to prepare for whatever Klaus has planned and Tyler faces his second transformation. The terrifying events quickly spin out of control, despite an unexpected act of courage. Finally, Damon admits the truth to Stefan about a terrible new development they must face...

Mystic Falls screens "Gone with The Wind" in the town square, and Damon's memories of Katherine in 1864 mix with the reality of present-day Elena. Stefan pays a steep price after trying to prevent a tragedy, and Sheriff Forbes makes a dangerous mistake while trying to keep everyone safe. Multiple lives hang in the balance as the consequences of the sacrifice ritual play out to a horrifying conclusion.