Season three's epic finale had left many fans awe-struck. Not only were the Castor clones eliminated (except Mark), but Sarah also got her hands on the original and a new villain emerged. Neolution was the main theme in the show's first season and it now seems that the Neolutionists have infiltrated Topside, Castor and Leda. So what can fans expect from season four?

Co-executive producer Graeme Manson spoke to TVLine about the upcoming season of "Orphan Black". In the interview, he did not give particulars about Delphine's fate, who was mysteriously shot in the stomach after sharing a (seemingly) last kiss with long-time love Cosima. However, the showrunner did make it clear that the Neolutionists would be the next big bad of "Orphan Black".

He explained, "It's doubling back to the very beginning and the first face we saw of Neolution, which was the sort of pop-culture Dr. Leekie face. That philosophy appears to be far more deep-rooted than we've known so far. That's the journey we're going to go on next season."

Moreover, season four will address the question of how Charlotte landed up with the Neolutionists. The last that viewers saw of her was when she was in the custody of Marian. The executive producer said that Marian is not a neolutionist, and the story of how and why Charlotte is now with them will be explored.

Fans will see more of Mark, the only Castor clone who helped Leda, and Krystal, the suspicious Leda clone who was put in place of Rachel.

In another interview with co-executive producer John Fawcett, published by Zap2it, the showrunner says that Sarah and Art will don their detective hats. "...we could reset a little bit and go back to Sarah doing some good ol' police work and working with Art...and trying to figure out who...Neolution really is and get to the bottom of the real mystery behind this."