(Spoiler Alert !) Three bloodsuckers were found in Chicago and Klaus will find every way to create a hybrid.

Stefan and Klaus were at windy city, where he reunited with Klaus baby sister, Rebecca, who fell in love with Stefan in 1920s.

Klaus went to Chicago to look for the Original Witch and to consult his dilemma of not being able to create hybrids. The witch, Gloria, needed a necklace Rebecca once wore but lost. Klaus resurrected Rebecca to redeem the necklace. The necklace is currently in the possession of Elena when Katherine gave it to her.

In an interview, Nina Dobrev said that this episode caused lasting changes to Elena's character. "Because of what happens with Stefan, she learns how to fight and become a warrior," says Dobrev. "This is the season where Elena stops letting the boys in her life dictate what happens."

What happened is that Elena found Stefan's old diary and discovered that it took Lexi almost 13 years to make Stefan not like human blood and another 30 years to make him normal. This enlightened Elena when Stefan said to her to stop what she is doing and to let him go.