CBS has released a new plot synopsis for an upcoming episode of CBS's The Big Bang Theory, with significant storylines for Howard (Simon Helberg) and Penny (Kaley Cuoco-Sweeting), plus a surprise cameo.

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Episode 8.15 of The Big Bang Theory is titled The Comic Book Store Regurgitation and according to the new CBS plot synopsis, it will be an action-packed episode.

"Wolowitz receives some shocking news as everyone prepares for the reopening of Stuart's [Kevin Sussman] comic book store," the synopsis reads. "Penny teaches Sheldon how to 'let it go,' but can't follow her own advice after she learns something infuriating about Amy [Mayim Bialik]. Also, Leonard [Johnny Galecki] and Raj [Kunal Nayyar] think they spot Nathan Fillion at a restaurant."

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The information about Howard's shocking news as well as the Fillion cameo have already been revealed, though the Penny storyline is new. It remains to be seen what Penny will be so mad at Amy about, though it could have something to do with her slighting her in some way.

As for the other key storylines, the Howard plot-line has to do with his mother, Mrs. Holowitz, who was played by the late Carol Ann Susi. It has been reported that this will be the episode that pays tribute to her, so this may be an emotional one for the cast and the audience watching.

On a happier note, Fillion's cameo involves him playing himself and eating at a restaurant where Leonard and Raj spot him and approach him carefully for a picture.

The episode is slated to air Thursday, Feb. 19.

The Big Bang Theory airs Thursdays at 8 p.m. ET/PT on CBS.

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