New Details Revealed About 'Grey's Anatomy's Fall Finale

Grey's Anatomy fans may have enjoyed a nostalgia-soaked walk down memory lane during last week's milestone 300th episode, but they can expect a totally different change of pace during this week's fall finale.

Thursday's episode finds Grey Sloan's entire computer system down after being hacked, causing chaos and panic throughout the entire hospital. Co-showrunner Krista Vernoff calls the episode an "edge-of-your-seat action movie," but admits that she needed convincing from writer William Harper.

"When Bill pitched me the hacking [story] I said, 'Don’t we usually do some great big giant storm or something?'" she told TVLine. "And he said, 'This is a great big giant storm. When people hack hospitals it is a life and death storm.' It’s incredible what he’s done. It’s completely different tonally from last week’s episode."

Co-star Kevin McKidd, who directed the episode, calls it "kind of like Speed [without] the bus," adding, "It’s a moving freight train, and then it hits this point at the end of the episode where you’re like, ‘What’s going to happen?’ It really is a classic and beautifully done cliffhanger episode."

The suspenseful episode would be totally different from the previous 300th installment, in which longtime fans were treated to a nostalgic tribute to all the 299 episodes that came before it. The nature of the milestone episode had fans speculating how the series would eventually end, with one fan theory in particular taking the spotlight.

The sad theory suggests that the series would end with Meredith Grey having Alzheimer's disease, and her voiceovers from every episode would turn out to be her telling her three adult children stories from her days working in the hospital — not unlike the pilot episode where Meredith’s voiceover narration was revealed to be a story she was telling her mother (who had Alzheimer's) at an assisted living facility.

Assuming some of future Meredith's memories were altered by Alzheimer's, some of the crazy story lines from years past could end up being the result of Meredith's alternate reality. Whether or not that fan theory will pan out is a mystery, as Grey's is still going strong, and will continue to do so as long as Ellen Pompeo (Meredith) wishes.

“Ellen and I have a pact that I'm going to do the show as long as she's going to do the show," series creator Shonda Rhimes told E! News.

“So the show will exist as long as both of us want to do it. If she wants to stop, we're stopping. So I don't know if we'll see 600, but I want to keep it feeling fresh. As long as there are fresh stories to tell and as long as we're both excited about the stories being told, we're in. So, we'll see where that takes us," Rhimes added.