The Vampire Diaries 4×21 “She’s Come Undone” – Damon (Ian Somerhalder) and Stefan (Paul Wesley) try a brutal new approach to provoke Elena (Nina Dobrev) into turning her humanity back on, and Caroline (Candice Accola) 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 (Zach Roerig) gives Rebekah (Claire Holt) some unsolicited advice on her life choices, and she tries to help him in return. Caroline has a confusing and dangerous encounter with Klaus (Joseph Morgan), and Katherine (Nina Dobrev) is suspicious when Bonnie (Kat Graham) makes her an offer that she promises will benefit them both. Darnell Martin directed the episode written by Michael Narducci & Rebecca Sonnenshine (#421).