Spoiler TV has posted a synopsis for season 4 episode 20 of The Vampire Diaries titled, The Originals:

Acting on a mysterious tip that a plot is brewing against him in New Orleans, Klaus (Joseph Morgan) makes a trip to the town he and his family helped build. Klaus’ questions lead him to a reunion with his former protégé, Marcel (guest star Charles Michael Davis), a charismatic vampire who has total control over the human and supernatural inhabitants of New Orleans. Determined to help his brother find redemption, Elijah (Daniel Gillies) follows Klaus and soon learns that Hayley (guest star Phoebe Tonkin) has also come to the French Quarter searching for clues to her family history, and has fallen into the hands of a powerful witch named Sophie (guest star Daniella Pineda). Meanwhile, in Mystic Falls, Damon (Ian Somerhalder) and Stefan (Paul Wesley) continue with their plan for Elena (Nina Dobrev), while Katherine (Nina Dobrev) reveals a surprising vulnerability to Rebekah (Claire Holt) and asks her to deliver a message.