Summer Glau is set to return as Kendall Frost in an upcoming Season 8 episode of "Castle," when she will again try to outshine series co-star Nathan Fillion.

TVLine reports Glau has inked a deal to guest star opposite Fillion in Episode 14 of the spring season of the long running series. Glau will play a provocative private investigator from Los Angeles who directly competes against Castle to solve a deadly mystery.

The two actors also recently teamed up for an episode of fellow "Firefly" star Alan Tudyk's web series "Con Man." Glau is now the third "Firefly" alum to co-star with Fillion on at least one episode of "Castle," joining Gina Torres and Adam Baldwin.

Glau's TV credits also include "The Sarah Connor Chronicles," "Dollhouse," "Alphas" and "Arrow."

CarterMatt predicts the upcoming episode stands to be a comedic one, as Glau has previously shown off her "comedic chops" over the years. How that all fits into an episode that will also involve the NYPD remains to be seen.

"Castle" returns to the airwaves on Feb. 1. In the mid-season premiere, Rick will work side by side with his daughter Alexis (Molly Quinn).

TVLine reports the father and daughter duo travel to California in the episode to work at solving a murder that leads them right back to New York. Before the case is solved, chances are Castle will also be seeking assistance from NYPD wife Kate (Stana Katic).

Word is the next several episodes are also slated to delve into the ongoing mystery of Rick's Season 7 disappearance.

"We haven't nailed the story down for it," executive producer Alexi Hawley recently said of rumors his disappearance will somehow be connected to his wife. "But we do like the idea that something that Castle came across during his missing time is actually why his memory was wiped."

Related