Last week, Rebekah (Claire Holt) was possessed by her mother Esther (Alice Evans). She is currently working with Alaric's (Matt Davis) evil alter ego to bring about the death of the Originals.
However, the executive producer has insisted that the outcome of the possession will not be predictable.
"That storyline takes instantly a left turn right at the beginning of the episode," Plec told Entertainment Weekly.
"So everything everybody thinks they're gonna see is actually different."
Plec recently revealed that she knows how the show will end after penning the series final scenes with fellow executive producer Kevin Williamson.
"We were tired and stressed and talked about the last character moments of the show," she explained. "[We] both started crying... and just felt like [the idea] was right."
The Vampire Diaries airs Thursdays at 8pm on The CW.