Supernatural's Men of Letters bunker is one of the few permanent sets for the CW drama but it will come close to destruction during "Slumber Party."

Airing as the fourth episode of season 9, "Slumber Party" contains a superabundance of interesting plotlines. From the return of Charlie Bradbury (Felicia Day) to a look at the history of the Men of Letters to the appearance of the Wizard of Oz's Dorothy (Tiio Horn), the Robbie Thompson ("Pac-Man Fever," Goodbye Stranger") penned script promises an exciting Halloween week installment.

Sam (Jared Padalecki) and Dean (Jensen Ackles) will call on the tech-savvy Charlie when they try to use an old Men of Letters computer to track the whereabouts of fallen angels, according to Spoiler TV. However, as they move the ancient piece of technology, a hexbag will be disturbed thus releasing a web in which Dorothy had trapped herself and the Wicked Witch (Maya Massar).

This new revelation will result in flashbacks to the early history of the Men of Letters and their secret lodgings.

"We'll discover how far the Men of Letters reach back into the Winchester's family history," said executive producer Jeremy Carver in the TV Guide Comic-Con edition. "And they'll be a source of new characters and [storylines]."

One of these new characters will be Plays Haggerty, a 1930's member of the now defunct secret society, according to The Hollywood Reporter.

"We very early on have a fun but surprising episode involving the Men of Letters where we'll actually see the first two Men of Letters going to, literally turning the key for the first time in 1935," Carver told the Examiner. "You're going to see that case as something really wonderful to do with The Wizard of Oz."

Check out the Winchester brothers' discovery of the Men of Letters bunker in the video below.

Supernatural airs Tuesdays at 9 p.m. ET on the CW.

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Supernatural, The cw, Television