[s1e15] Masquerade -

This episode is a high-stakes turning point where the main cast finally coordinates to take down Katherine Pierce.

Katherine has a witch named Lucy cast a binding spell, linking Katherine’s physical body to Elena’s. Every injury Stefan and Damon inflict on Katherine is mirrored on Elena, forcing them to stop their attack. [S1E15] Masquerade

Alaric attempts to kill Damon but is killed himself. He remarkably comes back to life, revealing for the first time the power of his protective Gilbert Ring. This episode is a high-stakes turning point where

Damon participates in a fundraising auction, using the platform to taunt Alaric about his "delicious" wife. Alaric attempts to kill Damon but is killed himself

Lucy reveals herself as a distant relative of Bonnie Bennett and turns on Katherine once she realizes Bonnie is "one of the good ones". She breaks the link and hands the moonstone to Katherine, but also incapacitates her.

Elena discovers that her birth mother, Isobel, was Alaric Saltzman's wife and was turned into a vampire by Damon.