The second season begins with Elena discovering her uncle John's bloody body and learning Jeremy's fate, and Damon realizing that Katherine has returned. Meanwhile, Caroline is taken to the hospital following a car accident, and Tyler's mysterious uncle Mason arrives in town.

When a confused and desperate Caroline leaves the hospital and joins her friends at the Mystic Falls Carnival, Damon wants to take immediate action, but Stefan and Elena come to Caroline’s defense. Matt is completely mystified by Caroline’s behavior, but still tries to tell her about his feelings for her.. Damon has suspicions about Tyler’s Uncle Mason and uses Tyler’s volatile personality in an attempt to get Mason to reveal his secret. Upset with everything going on around her, Bonnie takes her anger out on Damon.

Elena, Damon and Alaric take a road trip to Duke University and search through Isobel’s research on folklore and paranormal phenomena to see if they can uncover any clues to the mystery surrounding the Lockwood family. Isobel’s former student, Vanessa offers to guide them through the research and ends up getting quite an education herself. Stefan comes face to face with a terrifying new danger in the woods, and Tyler makes a shocking discovery about Mason.....

Stefan takes drastic measures to find out the real reason Katherine has returned to Mystic Falls, and is shocked when she reveals new secrets about what really happened in 1864. Damon tries a new tactic to resolve his issues with Mason,.... but it proves costly. Tyler pushes Mason to tell him the truth about the Lockwoods. Finally, when Katherine delivers an ultimatum, Stefan and Elena are left with very few options.

Tyler learns more about the Lockwood family curse from Mason. Stefan and Damon argue over how to handle Mason. Elena tries to keep Jeremy from becoming more involved with the Lockwood mystery, but Jeremy makes an effort to hang out with Tyler. Mason gives Sheriff Lockwood some startling information, leading to a night of violence, confession and heartbreak.

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.

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.

On the first day of their senior year, Elena, Caroline, Bonnie and Matt are still reeling from recent events, while Tyler seems to be enjoying everything a little too much. Damon is annoyed by a new houseguest, and everyone is surprised by the arrival of a new student in Alaric's history class. Matt asks Bonnie for help when he realizes he made a serious mistake. Meanwhile, Stefan continues to carry out his latest assignment from Klaus.

As Mystic Falls prepares to celebrate the traditional Illumination Night, the town is invaded by spirits of the dead. After a particularly violent encounter with an angry spirit, Damon asks Bonnie to find the reason behind the ghosts' surprising power. Elena convinces Jeremy to use his connection to the other side to help her find a new way to reach Stefan, leading Jeremy to a terrible choice. Finally, Alaric discovers a long-hidden clue to the past.