Love Lust abounds on Mistresses, but which of the leading ladies is spicing things up in the bedroom?

While three of the four women end up getting down at some point in Thursday's episode, it's Karen (Yunjin Kim) who finds herself in an unexpected entanglement with Vivian (Sonja Bennett) and Alec (Ed Quinn). (By the way, you'll get a tease of the threesome at the end of this week, but you'll have to wait until next week to see the real fun in the bedroom.)

But this isn't just a one-night stand. Karen, who has a history of being with unavailable men, finds herself falling for both of them, testing the waters for a polyamorous relationship! "Throughout the season, it's really about the love between the two women [and] she's very confused by it," Kim says. "She's someone who's never had an experience with a woman, and not just a woman but also [her husband]. So it's going to get messy and clunky... and it doesn't settle until the very last episode."

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So how will her best friends April (Rochelle Aytes) and Joss (Jes Macallan) handle the news? "April, being who she is, she's stunned and not comfortable with ... the polyamorous relationship and Jos gets too busy with her world." Kim is curious how viewers will react. "It's a world that hasn't been explored much on a network show and [we've] been daring and open," she says. "After this season, I'm surprised by the stuff we've been able to show!"

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Mistresses airs on Thursdays at 9/8c on ABC.

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Watch an exclusive sneak peek of Karen and Vivian: