As season two begins, the action picks up on the same night as last season's finale, and Elena arrives home to a nightmare. Damon is the first to realize Katherine has returned.

When a confused Caroline leaves the hospital and joins her friends at the Mystic Falls Carnival, Damon wants to take action, but Stefan and Elena come to Caroline's defense.

Elena, Damon and Alaric go to Duke University to search through Isobel's research, hoping to uncover any clues surrounding the Lockwood family. Plus, Stefan faces a new danger.

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 (recurring guest star TAYLOR KINNEY), but it proves costly. Meanwhile, Tyler pushes Mason to tell him the truth about the Lockwoods, and when Katherine delivers ...

Tyler learns more about the Lockwood family curse from Mason (recurring guest star TAYLOR KINNEY). 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 (recurring guest star MARGUERITE MacINTYRE) some startling information, leading to a ni...

Despite Elena's efforts to keep Jeremy safe, he offers to help Damon and Alaric deal with Katherine. Sheriff Forbes (recurring guest star MARGUERITE MacINTYRE) and Caroline share a few rare moments of quality mother/daughter time. Bonnie accidentally discovers new information about Mason (recurring guest star TAYLOR KINNEY) and shares it with Stefan, which leads to Damon taking matters into his...

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 (guest star NATASHIA WILLIAMS – Romeo!, She Spies), 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...

Stefan and Damon come to Elena's assistance and, in the process, learn surprising new information. Jeremy helps Bonnie after she casts a difficult and exhausting spell.

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 newfound confidant to help him try to discover the real purpose and power of the moonstone. Jeremy and Bonnie meet Luka Martin (guest star BRYTON JAMES -- The Young and ...

Elena decides to take matters into her own hands and offers a tempting incentive to Rose (recurring guest star LAUREN COHAN) 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 dang...

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 (recurring guest star MICHAELA McMANUS -- One Tree Hill, Law & Order: Special Victims Unit) shows up in Mystic Falls, searching for her missing friend, Mason. Elena is frus...

Stefan has his own ideas about Elena's new plan for the future. While Damon tries to get the truth out of Jules (recurring guest star MICHAELA McMANUS), he asks Elena to keep an eye on Rose (recurring guest star LAUREN COHAN), 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 come...

Johnathan Gilbert's (recurring guest star DAVID ANDERS) 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 (recurring guest star Randy Goodwin -- Girlfriends). Plus, ...

Stefan and Elena attempt a romantic weekend getaway, not realizing that they've been followed. Damon attends a tea at the Historical Society to talk to Elijah (DANIEL GILLIES).

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 (recurring guest star BRYTON JAMES), Jonas (recurring guest star RANDY GOODWIN) makes his feelings clear to Bonnie and Jeremy. Trying to catch Elijah (guest star DANIEL GILLIES) off-guard, Damon arranges a dinner party for him with Jenna, Alaric a...

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. Meanwhile, Stefan and Bonnie try t...

Elena and Alaric lash out at John (DAVID ANDERS) when Isobel's (MIA KIRSHNER) unexpected arrival leaves Jenna devastated. Stefan and Damon realize they have a new secret weapon.

Elena receives disturbing messages from Klaus. Expecting him to show up at the "1960s Decade Dance," Damon and Alaric attend as chaperones, but Klaus is playing a complicated game.

Klaus (JOSEPH MORGAN) is revealed and Elena learns shocking news about his motives. Plus, flashbacks to 1491 reveal Katherine's introduction to Elijah (DANIEL GILLIES) and Klaus.

Damon is willing to go to great lengths to prevent Elena from being a victim of Klaus's (JOSEPH MORGAN) plan to break the curse, putting him at terrible odds with Stefan.

As the full moon arrives, Elena prepares for whatever Klaus (JOSEPH MORGAN) has planned and Tyler faces his second transformation. The terrifying events spin out of control.

Lives hang in the balance as the consequences of the sacrifice ritual play out.