Klaus and Stefan arrive in Chicago, where Stefan is reunited with a vampire who hasn't really moved on from her interest in him decades earlier. In a flashback to Chicago in the 1920s, Stefan comes face-to-face with a shocking chapter from his wild past. After Damon gets a tip on Stefan and Klaus' whereabouts from an unexpected source, he and Elena follow their trail. Back in Mystic Falls, Tyler is concerned about Caroline and turns to Sheriff Forbes for help.

Elena is surprised to receive an invitation to a formal ball, and when Damon and Stefan hear the party is being hosted at Klaus’s newly renovated mansion, they both insist on attending the event with her. Caroline and Matt also receive invitations to the ball from unexpected admirers. At the elegant party, Elena learns of a horrifying plan that could lead to numerous deaths and she must decide who she can trust with her new information. Caroline discovers a side of Klaus no one would have suspected. Finally, after an evening of violence and dashed hopes, Damon finds a new way to cope.

Elena and Damon set off together to make sure Jeremy is safe in Denver, and to see if his special abilities can help reveal the information they need about ancient vampire bloodlines. It doesn’t take them long to learn that Jeremy has been hanging with the wrong people. Stefan and Klaus both go to brutal extremes in their search for the missing weapon. Caroline is thrilled when Tyler returns to town, but Tyler soon suspects that something has been going on between Caroline and Klaus. Matt has his hands full trying to keep Rebecca busy organizing the school’s upcoming 1920s Decade Dance.

Klaus acts on his intentions to leave town with Elena, but finds resistance from a surprising new enemy. Bonnie calls on Abby to help her with a difficult spell. As events spiral out of control, Elena is determined to protect Caroline, Damon and Stefan enlist Tyler’s help, while Bonnie and Jeremy take a terrifying risk to make sure her spell is effective. Damon and Stefan have a surprisingly candid conversation about the future.

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.

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.

When an impulsive decision by Damon threatens to unravel a carefully negotiated deal between Stefan and Lily, he has no choice but to make amends with his mother before things spiral further out of control. However, Lily remains one step ahead and carries out a harsh plan that hits Damon where it hurts most.

Elsewhere, after returning to Whitmore Collage, Alaric turns to Bonnie for help with a mysterious and potentially dangerous artifact he has obtained, while Matt is forced into making a risky life or death decision. Meanwhile, Caroline, who finds herself a pawn in Lily and the heretics' plan for retribution, uncovers a shocking detail about Stefan's past.

When Enzo’s efforts to protect Bonnie end up putting her life in jeopardy, they learn that Rayna may hold the key to her survival. With time running out and Rayna at the reins, Enzo and Bonnie reluctantly team up with Damon, who is desperate to save Bonnie’s life and to repair their broken friendship.

Elsewhere, when Stefan travels to Dallas and comes face to face with Alaric, tensions escalate and they are forced to confront the fallout from Stefan’s absence in Caroline’s life. Finally, Enzo learns The Armory’s true motives behind their search for Bonnie.

A wedding is quickly planned in order for Damon and Stefan to lure a dangerous enemy out into the open. This looming threat puts the fate of Mystic Falls in eminent danger and must be destroyed.