Changes are afoot, as is Nathan Fillion, when The Big Bang Theory season 8, episode 15 airs tonight.

The episode, titled “The Comic Book Store Regeneration,” will feature surprises and disappointment for the geeky gang.

“Wolowitz receives some shocking news as everyone prepares for the reopening of Stuart’s comic book store,” CBS says. “Penny teaches Sheldon how to ‘let it go,’ but can’t follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they spot Nathan Fillion at a restaurant.”

Mind games were also an issue on the latest episode of The Big Bang Theory. Leonard and Sheldon published a paper on some physics thing, which drew a largely positive response – but one trolling commenter nearly destroyed everything. Turned out it was Stephen Hawking, so no big deal. Meanwhile, Penny, Amy, and Bernadette shared embarrassing truths, old secrets, and sexy fan fiction.

The preview for “The Comic Book Store Regeneration” makes it seem like Sheldon’s frustrations with change will once again be an important focus.

Two sneak peeks from The Big Bang Theory season 8, episode 15 focus on the changes in question. First, Sheldon questions Amy’s decision to Science with his rival, Barry Kripke.

And in the second sneak peek, Howard finds himself unnerved by an unexpected addition to Stuart’s new comic book store.

Uh-oh, Stuart. Do not insult the clown art.

That being said, the still photos from tonight’s episode of The Big Bang Theory suggests that none of these problems are remotely as exciting as a selfie with Castle and Firefly star Nathan Fillion.

Where to watch ‘The Big Bang Theory’ season 8, episode 15 online:

Catch The Big Bang Theory season 8, episode 15 on CBS.com. New (and old) episodes are also available for purchase on Amazon and iTunes.

The Big Bang Theory season 8, episode 15, “The Comic Book Store Regeneration,” airs tonight at 8:00 p.m. on CBS.

What are your hypotheses for ‘The Comic Book Store Regeneration’?