Kara, Hank, Alex and Maggie will uncover a top secret in the upcoming episode of "Supergirl" season 2.

Titled "Survivors," the new episode will follow Kara and her friends as they find out about the underground alien fight club of the National City. The synopsis for the episode reveals that Kara and Alex will be the first to discover the alien fight club while they investigate the killing of an unregistered alien.

In the trailer for the episode, Alex and Maggie go undercover to get more information about the fight club, where aliens kill one another to entertain rich humans. The video shows the two masquerading as wealthy patrons of the club while witnessing Miss Martian face off against another alien refugee. The clip shows that upon hearing the news from Alex and Maggie, Hank will visit Miss Martian to pressure her to reveal the person who runs the fight club.

"She calls herself Roulette. She has powerful friends!" Miss Martian tells Hank in the clip. 

The clip also reveals that as Supergirl tries to close down the club, she will find herself trapped inside the death match cage with an alien who seeks to take her down.

In the comics, Roulette is also known as Veronica Sinclair and is one of the enemies of the Justice Society. She is notorious for running a gambling establishment for supervillains, where they can bet on various events. She is portrayed as a cunning, business-minded character who manipulates others for her own gain.

"Supergirl" season 2, episode 4 airs on October 31, 8:00 P.M. on The CW.