ET has an exclusive look at Sunday night’s episode of The Librarians, and there’s a pretty big threat lurking about!

When students start disappearing at Wexler College, the Librarians arrive to discover some very bizarre occurrences involving an aptly named "tentacle monster."

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The series, which is now in its second season, centers around an organization hidden below the Metropolitan Public Library, dedicated to protecting the world from secret, magical occurrences that happen on a daily basis.

The Librarians stars Rebecca Romijn, Christian Kane, Lindy Booth, John Kim and Noah Wyle.

You can catch the giant "tentacle monster" when the new episode airs Sunday at 8pm PST on TNT.