Where does Castle possibly go after a third season finale that promised game-changers and delivered and then some, making for one of its best episodes yet?

Look for the series to begin a newly complex and richer chapter next fall as the relationship between Castle and Beckett evolves, creator Andrew Marlowe tells EW.

“I think [the finale] was a great way to chapter out on the early portion of the Beckett-Castle relationship and to transition us to the even more complex more mature aspects of their relationship as we move forward,” Marlowe said.

“I think that even though Castle is still kind of a charming, boyish man, we see an enormous amount of growth in him over the last three years towards a kind of maturity. It doesn’t mean Castle’s going to lose his boyish charm."

"It just means that he’s becoming more complex and interesting. The same with Beckett, a character who started off being relatively closed off.”

Specifically, Marlowe pointed to the scene in the finale where Montgomery tells Beckett that she “wasn’t having any fun” before Castle came along as an example of the kind of growth he likes to see from the pair.

“We’ve really seen her start to open up to both Castle and to the audience, and there are more mysteries to mine in both of these characters, as there are in the secondary characters, but I think that this marks a new and different chapter in their relationship."

"We’re not looking to fundamentally change the show, we’re just looking to enhance it and make the experience even richer and more satisfying for the fans.”

For more on next season, check out these Castle Season 4 spoilers!

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.