"Castle" star Stana Katic is billing Season 8 of the ABC-aired drama series as a "nail-biter."

Katic, who stars as Det. Kate Beckett, recently took to Twitter to post, "Had a great mtg w @AlexiHawley & @OldManWinter14 about S8! (Nail-biter) Love #Castle cast&crew. Looking forward to playing together again."

Speculation has also been rampant the new season could bring about a dramatic change in the relationship between Beckett and Nathan Fillion's Castle.

CarterMatt reported a new character known as Hayley will be joining the cast and will garner much of Castle's attention. Meanwhile, rumors are Beckett could be headed for a dive into the world of politics.

That very prospect was teased during Season 7's finale when a colleague implored her to move in that direction instead of trying to take another step up within the ranks of the NYPD.

In a recent interview with Entertainment Weekly, new co-showrunner Alexi Hawley hinted that change could be coming to the series.

"We just want to get in there and try to tell some really dynamic stories," he said. "Going into Season 8, it feels like it's time to shake things up a little bit."

Things are starting to settle in for the upcoming season after a period of uncertainty where it wasn't even known if the series' stars would be making a return engagement.

Both Katic and Fillion's contracts expired at the end of last season, and while Fillion re-signed relatively quickly, doubts persisted about Katic.

Finally, after much haggling, the two sides reached agreement on a new one-year deal.

"Castle" Season 8 premieres on Sept. 21 on ABC. The series also stars Seamus Dever as Kevin Ryan, Molly Quinn as Alexis Castle, and Jon Huertas as Javier Esposito.