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.

Stefan is shocked when Katherine reveals new secrets about what really happened in 1864. Damon tries a new tactic to resolve his issues with Mason (TAYLOR KINNEY).

Stefan is shocked when Katherine reveals new secrets about what really happened in 1864. Damon tries a new tactic to resolve his issues with Mason (TAYLOR KINNEY).

Tyler learns more about the Lockwood family curse from Mason (TAYLOR KINNEY) and Sheriff Lockwood (MARGUERITE MacINTYRE) receives startling information.

Katherine chooses a new victim. Bonnie discovers new information about Mason (TAYLOR KINNEY) and shares it with Stefan, which leads to Damon taking matters into his own hands.

Stefan and Damon decide on a new plan to deal with Katherine at the Lockwood's masquerade ball. Things take an ugly turn when Matt and Tyler start doing shots with their friends.

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 searching for the truth about Katherine's past. Jeremy and Bonnie meet a new student (BRYTON JAMES) with a surprising family history.

Jeremy's reckless attempt to help Bonnie lands him in a life-threatening position and forces Stefan to put himself in danger. Bonnie and Luka (BRYTON JAMES) become closer.

As the full moon nears, Caroline helps Tyler prepare for transformation. Damon and Alaric are suspicious when a stranger named Jules (MICHAELA McMANUS) shows up looking for Mason.

While Damon tries to get the truth out of Jules (MICHAELA McMANUS), he asks Elena to keep an eye on Rose (LAUREN COHAN), a situation that turns unexpectedly dangerous.

As the full moon nears, Caroline helps Tyler prepare for transformation. Damon and Alaric are suspicious when a stranger named Jules (MICHAELA McMANUS) shows up looking for Mason.

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 his darkest days. Trying to catch Elijah (DANIEL GILLIES) off-guard, Damon arranges a dinner party for him with Jenna, Alaric and Andie (DAWN OLIVIERI).

Stefan and Bonnie try to convince Jonas (RANDY GOODWIN) and Luka (BRYTON JAMES) they should all be working together, but Jonas' lack of trust leads to a violent confrontation.

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.

In the season finale, more than one life hangs in the balance as the consequences of the sacrifice ritual play out to a horrifying conclusion.