04/19/2012 09:49 am ET

'The Secret Circle': Cast Talks 'Crystal' And The Other Blackwell Child Reveal

When HuffPost TV visited the Vancouver-based set of "The Secret Circle" the cast was in the midst of filming the April 19 episode, "Crystal," in and around a disused mine.

As we discovered in the March 29 episode, the circle is in desperate need of each family's crystal if they hope to protect themselves against demon-fueled witch hunter Eben and his cronies. By our count, Cassie (Britt Robertson) and Ethan (Adam Harrington) hold two of the crystals (presumably the Blake and Chamberlain stones), while Dawn and Charles drained the power of a third. "Crystal" will deal specifically with the Armstrong and Glaser gems, as Chris Zylka (Jake) and Jessica Parker Kennedy (Melissa) previewed for us on set.

"My grandmother is a witch and she is a holder of one of our crystals, which we desperately need to get," Parker Kennedy explained. "We kind of need to be sneaky and go around her because she would never give it to us -- to protect us, of course, because she thinks if it’s in our hands it could cause bad things to happen." While we won't get to see Melissa's grandmother on-screen, we will be introduced to Jake's grandfather, played by veteran genre actor John de Lancie

"I was so excited that he got cast, and then we shot him out in one day. It was like, 'Oh, man,'" Zylka laughed. "But watching that man do a scene was literally like watching an acting class."

As for what the relationship between Jake and his grandfather is like, Zylka teased, "The Armstrongs are definitely different. We’ve gone to my grandfather’s to try and locate the Armstrongs' crystal, because it’s pretty clear he’s the only family member I have left. [Laughs.] Let's just say he's not gonna make it easy to find the crystal. Grandpa Royce is a little insane, and definitely a conspiracy theorist. He’s gonna feed a lot of information that the fans have been waiting to hear, and maybe bring on some new things into the game."

The episode will also feature the return of Callum (Michael Graziadei), the dastardly Devil's Spirit dealer who led Melissa astray earlier in the season. "Yes, Callum, my dear old flame, comes back and wants to steal one of our crystals," Parker Kennedy previewed. "We’re in desperate need of finding all the crystals so that they can come together and we can each have our individual powers. Callum comes and tries to steal them. He wants to sell one, so he’s causing a ruckus. We end up in these crazy mines ... Adam [Thomas Dekker] and Melissa do some serious ass-kicking together in the mines, which is gonna be really fun."

Parker Kennedy also told us that "there’s a lot more light shed into the Blackwell family" this week, as the identity of the other Blackwell child will finally be revealed. There's a good case to be made for all three of Cassie's female friends to be her secret sister; Faye's mother Dawn has an undeniable chemistry with Blackwell, Diana has always had a sibling-like bond with Cassie, and we know very little about Melissa's family in general, leaving lots of blanks to be filled in. Parker Kennedy didn't know much more than us about her family tree, but could share a few clues: "I don’t have any kind of idea who my parents are. I know that my mother died when I was young and I live with my father and my stepmother who I’m very close to, apparently, but I don’t know their involvement in the [magic] world. My father obviously knew what was going on [with the last circle], so I assume my father is [a witch] and I know my grandmother is, and hopefully, that’ll unravel later on."

Naturally, the cast remained tight-lipped on who Cassie's long-lost sibling could be, but there's certainly one circle member who may be rooting for a connection to the dark bloodline more than others ...

"Faye has a feeling that she could be the other Blackwell daughter, so in the back of her head she's thinking there’s a chance that she and Cassie could be sisters," Phoebe Tonkin, who plays Faye, revealed. "Faye would like to be the sister, but there’s a good chance that she could be disappointed. She’s attracted to dark magic, she’s attracted to solo magic, so with the idea that there could be another circle member that could have dark magic like Cassie, she's like, ‘Right, I’m gonna find out how this could be me.’"

Do you think Faye could be the second Blackwell child, or are you rooting for one of the other circle members? Don't miss "Crystal," airing April 19 at 9 p.m. ET on The CW, when all will be revealed.