The Vampire Diaries, Know Thy Enemy

Elena arrives home to a nightmare, as she discovers the fate of Uncle John and Jeremy. Sheriff Forbes waits to hear if her daughter Caroline will survive the car accident. Damon is the first to realise 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 defence.

Elena, Damon and Alaric go to Duke University to read Isobel's research, hoping to find clues about the Lockwood family. Stefan faces a new danger.

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. Tyler pushes Mason to tell him the truth about the Lockwoods.

Tyler learns more about the Lockwood family curse from Mason. Elena tries to keep Jeremy out of the Lockwood mystery, but he still meets with Tyler. Sheriff Lockwood receives startling information leading to a night of violence, confession and heartbreak.

Katherine chooses a new victim. Sheriff Forbes and Caroline share a few rare moments of quality mother/daughter time. Bonnie discovers new information about Mason and shares it with Stefan. Damon then takes matters into his own hands.

Stefan and Damon decide on a new plan to deal with Katherine at the Lockwoods' masquerade ball. Katherine calls on an old friend, Lucy, to attend the ball with her. Things take an ugly turn when Matt and Tyler start doing shots with their friends.

Stefan and Damon come to Elena's assistance and learn surprising new information in the process. Jeremy helps Bonnie after she casts a difficult, exhausting spell. Caroline does what she can to make things easier for Tyler.

Elena puts herself in a dangerous position searching for the truth about Katherine's past. Jeremy and Bonnie meet Luka Martin, a new student with a surprising family history. Damon looks into the moonstone's real purpose and power.

Jeremy's reckless attempt to help Bonnie lands him in a life-threatening position and forces Stefan to put himself in danger as well. Bonnie and Luka become closer. Tyler shows Caroline the Lockwood cellar, with terrifying results.

As the full moon nears, Caroline helps Tyler prepare for transformation. Damon and Alaric are suspicious when a stranger named Jules shows up looking for Mason. Elijah makes an unexpected appearance with an offer that could change everything.

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. Damon struggles to hide his emotions.

Johnathan Gilbert's return to Mystic Falls is an unhappy surprise to Elena, Jenna and Damon. Stefan does his best to reach out to a confused and conflicted Tyler. Jeremy comforts Bonnie after her disturbing conversation with Jonas.

Stefan and Elena attempt a romantic weekend getaway, not realising that they've been followed. Damon attends a tea at the Historical Society to talk to Elijah. Jenna starts to worry that Alaric isn't being honest with her.

Stefan tells Elena about his darkest days. 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.

Stefan and Bonnie try to convince Jonas and Luka they should all be working together, but Jonas' lack of trust leads to a violent confrontation. Frustrated with her relationship with Matt, Caroline finds a new way to get his attention.

Elena and Alaric lash out at John when Isobel's unexpected arrival leaves Jenna devastated. Stefan and Damon realise they have a new secret weapon. Bonnie works with Damon and Jeremy to find the spell they'll need to harness her ancestors' power.

Elena receives disturbing messages from Klaus. Assuming he'll go to the '1960s Decade Dance,' Damon and Alaric attend as chaperones, but Klaus is playing a complex game. Bonnie reassures Jeremy that she can help Elena, but he asks Stefan for advice.

Elena learns shocking news about Klaus' motives. Flashbacks to 1491 show Katherine meeting him and Elijah and the origin of the moonstone curse. Disagreement over how to protect Elena leads to growing tension between the Salvatore brothers.

Damon is willing to go to great lengths to prevent Elena from being a victim of Klaus's plan to break the curse, putting him at terrible odds with Stefan. Stefan and Elena spend a romantic day together, afraid it might be their last.

As the full moon arrives, Elena prepares for whatever Klaus has planned, and Tyler faces his second transformation. The terrifying events spin out of control, and Damon admits the truth to Stefan.

More than one life hangs in the balance as the consequences of the sacrifice ritual play out to a horrifying conclusion. Sheriff Forbes makes a deadly mistake while trying to keep everyone safe.