S4, E19: After making a decision that infuriates Klaus, Elijah (recurring guest star Daniel Gillies) proposes a life-changing challenge for Rebekah (recurring guest star Claire Holt). Caroline finds that her carefully laid plans for the perfect Senior Prom night are disrupted by Elena, so she turns to an amused Klaus for a solution. Determined to get through to Elena, Damon and Stefan both attend the prom, but the evening begins to spiral out of control despite their efforts. When Elena suddenly lashes out in a way no one could have predicted, Matt turns to Rebekah for help. Finally, Bonnie makes a terrifying discovery, and Klaus receives a message that could change everything.