By Ken Tucker
March 09, 2009 at 07:55 PM EDT

Anyone who loved Joss Whedon’s short-lived series Firefly (2002) or its underrated movie adaptation Serenity (2005) will probably be watching some TV tonight, as two members of that cast, Nathan Fillion and Summer Glau, pop up in prime-time in new contexts.

Glau, now better known for a lesser show than Firefly, Fox’s Terminator: The Sarah Conner Chronicles, guest-stars as herself on Big Bang Theory. She’s a perfect object of adoration for the show’s lovable geeks:

Sight unseen (except for that clip), I’ll bet I’m going to enjoy tonight’s episode, given what a roll Big Bang has been on recently. (I am a member of my colleague Alynda Wheat’s campaign to get Jim Parsons an Emmy nomination.) It’s interesting the way Glau has achieved more success as a grim bombshell these days than she did as a waif-with-interesting-flaws as Whedon’s creation River. In fact, Glau’s glassy-eyed gaze in both Firefly and on Terminator can be seen as a precursor to the dazed-and-confused, “wiped” women of Whedon’s current series, Dollhouse.

Fillion, meanwhile, is starring in Castle, a too-playful-by-half cop-mystery series. In it, he plays a highly successful mystery writer who gets himself assigned to tag along with a cop (Stana Katic), ostensibly to research a new novel, but really because he thinks she’s cute. I gave the show a reluctant C- in EW‘s current “What To Watch” section, which pained me because I really like Fillion, but his charm is really squandered in a premiere episode whose lines are cute and predictable. But, given its plumb time period — Castle debuts right after the premiere of the heaven-help-us, highly-anticipated return of Dancing With The Stars — Fillion may end up with a ratings hit. Given his terrific work in the past (including Whedon’s Dr. Horrible Internet sensation), I can’t begrudge him any success, even if it’s in a vehicle that doesn’t match his talent.

Will you be watching Castle? Were you planning to watch Big Bang Theory anyway, or will you tune in especially to see Summer Glau?