Someone in The Librarians casting department is killing it at their job. Season 3 only started filming two weeks ago, and the TNT drama has already booked two of nerdom's biggest names.

Both Felicia Day (Supernatural, Eureka, Buffy the Vampire Slayer) and Sean Astin (The Lord of the Rings, The Goonies) will make appearances in episode 3. Titled "And the Tears of a Clown," the upcoming hour will see Jonathan Frakes of Star Trek: The Next Generation take the helm once more.

"What a gift," Frakes tweeted on Saturday. "My guest stars this week @feliciaday & @SeanAstin #TheLibrarians @LibrariansTNT."

Frakes isn't the only one pumped for Day and Astin to hit up the Portland set. Makeup artist Eva Lohse also geeked out over the news. "You guys. Episode 303s casting is more epic than the episode itself. And that's saying something," Lohse teased.

So, what will the beloved actors get up to once they enter the hallowed halls of the Library? That secret is still tightly under wraps, but it's a safe guess that showrunner Dean Devlin will play to the pair's comedic sides.

The Librarians stars Noah Wyle (Flynn), Rebecca Romijn (Eve), Christian Kane (Jake), Lindy Booth (Cassandra), John Harlan Kim (Ezekiel), and John Larroquette (Jenkins). Vanessa Williams will play the season 3 villain, joining the cast as General Rockwell. Leader of the Department of Statistical Anomalies, Rockwell will seek to capture the Librarians and uncover their carefully guarded catalog of magic.

Find out more when The Librarians returns to TNT this fall. Click the video below to see a preview for the series' latest episode.

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The Librarians, Television, TNT