Elena comes home to a nightmare; Damon realizes Katherine has returned; Tyler receives a surprise visit from his uncle.

When a confused and desperate Caroline leaves the hospital and joins her friends at the Mystic Falls Carnival, Damon wants to take immediate action.

Elena, Damon and Alaric go to Duke University to find Isobel's research into the paranormal and look for clues to the mystery surrounding the Lockwood family; Stefan faces a new danger in the woods; Tyler makes a shocking discovery about Mason.

Katherine recalls the past.

Tyler learns more about the Lockwood family curse from Mason, and Sheriff Forbes receives startling information.

Katherine chooses a new victim. Bonnie discovers new information about Mason and shares it with Stefan.

Stefan and Damon decide on a new plan to deal with Katherine at the masquerade ball.

Stefan and Damon come to Elena's assistance and, in the process, learn surprising new information.

As the full moon nears, Caroline helps Tyler prepare for his transformation. Meanwhile, Damon and Alaric are suspicious when a stranger shows up looking for Mason.

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.

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 Tyler.

Stefan and Elena attempt a romantic weekend getaway, not realizing that they've been followed. Damon attends a tea at the Historical Society.

Stefan tells Elena about his darkest days. Trying to catch Elijah off guard, Damon arranges a dinner party.

Katherine's mind games cause everyone frustration, but Elena, Stefan and Damon realise that her knowledge of Mystic Falls' history could be crucial to their survival.

Isobel unexpectedly returns, leaving Jenna devastated. Bonnie attempts to harness her ancestors' power. Stefan and Damon realise that they have a new weapon.

As the students get ready for a 1960s-themed dance at the school, Elena begins receiving disturbing messages from the ancient vampire Klaus from an unusual source.

Stefan and Damon are angry when they find out that Elena has taken matters into her own hands in the battle against Klaus. Tensions also rise between the brothers over the best way to protect her.

Damon reveals that he is willing to go to incredible lengths to protect Elena from falling victim to Klaus's plans. Stefan and Elena spend a romantic day together.

Despite an unanticipated act of courage, events spin out of control in a frightening way.

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