S04E21: She's Come Undone

Damon and Stefan try a brutal new approach to provoke Elena into turning her humanity back on, and Caroline is frustrated when her attempt to intervene backfires. When Elena figures out a way to call the Salvatore brothers' bluff, they call for backup from a surprising source. Matt gives Rebekah some unsolicited advice on her life choices, and she tries to help him in return. Caroline has a confusing and dangerous encounter with Klaus, and Katherine is suspicious when Bonnie makes her an offer that she promises will benefit them both.