There are only two episodes left before "Castle" wraps up its eighth season, and fans bid star Stana Katic farewell. The idea that these are the last few episodes of a fan favorite has lent a poignant feel to other humorous and engaging storylines.

The previous episode was a good example of everything that the show excels at — interesting plot, superb writing, fast pace, and great chemistry among characters. But as much as fans enjoyed watching Richard Castle (Nathan Fillion) and Kate Beckett (Katic) figure out who the real killer was while planning their date night, a lot of viewers also couldn't help but feel sad that the partnership between the two will soon come to an end.

The same might hold true for episode 21, even though the plotline hints at a fun-filled outing. The episode will apparently find an escaped psychiatric patient at Castle's office. But the axe-wielding inmate suddenly drops dead before he can do anything. The ensuing events and investigation lead to the writer suspecting that the victim's death might be the handiwork of the Antichrist.

A trailer for the upcoming episode, cheekily titled "Hell to Pay," begins with a shot of two women caught by surprise when someone smashes open their door. It's a man that Castle describes as a "knife wielding psychopath." Beckett examines the body and it's full of weird tattoos. Viewers then see a book that appears to be full of satanic images, as a worried Castle says he's being "targeted by dark forces."

The private investigator really seems to believe that he's cursed and appears to be jumpier and more paranoid than usual. His partner seems to enjoy this and pokes fun at him. The clip ends with Castle walking with Ryan (Seamus Dever) and Javi (Jon Huertas). While his two buddies tell him it's all in his head, a massive equipment suddenly falls down directly in front of them. The incident seems to further fuel Castle's belief that he has somehow been cursed.

The show's penultimate episode of the season seems lighthearted, but the same can't be said for the upcoming finale. "Castle" showrunner Terence Paul described episode 22 to EW as "an incredibly dynamic, big, large episode where Castle and Beckett are really tested."

"They have to call on all their friends — be it Espo, Ryan and Hayley — to help them take down the mysterious LokSat," Paul added.

While the idea of the LokSat mystery finally being resolved is compelling, fans are more concerned as to how the series will write off Beckett. With Katic no longer coming back for season 9, there are rumors that the character will be killed off, much to the dismay of the show's loyal viewers.

Episode 21 of "Castle" season 8 is set to air on May 9, 10 p.m., on ABC.