Things are about to get hot, hot, hot in the upcoming Season 3 installment of “Mistresses” titled “The Best Laid Plans.” But not in the way you would expect.

According to the promo video for episode 7, which is set to air Thursday, a couple of unsuspecting characters will lock lips in the forthcoming installment. The first duo teased to partake in a steamy rendezvous will be none other than Karen (Yunjin Kim) and Alec (Ed Quinn).

That’s right! The third has just become a primary! So how will twosome end up between the sheets without Vivian (Sonja Bennett)? Well, the trailer reveals Karen and Alec will end up getting hot and heavy in a supply closet after the doctor subtly reveals to Karen in his seductive voice that he knows how to please her.

“Karen enters into an uncharted territory in her relationship,” the summary reveals, suggesting Karen may struggle with the fact that she had singular sex. Does this mean Karen and Alec cheated on Vivian, a third member of their romance? Someone bring over the threesome rule book so we can find out!

Joss (Jes Macallan) will also find herself in a strange situation in episode 7 -- but for a good cause! See, Calista (Jennifer Esposito) is desperate to catch her lying, cheating, no good, husband partaking in infidelity so that she can divorce him and keep the empire she’s worked so hard for. According to Calista, if she was to leave Luca (Noam Jenkins) without proof that he cheated on her, then he could end up getting half of the profit she’s made. And we can’t have that, now can we?

So, what does Joss do to help out her friend? She poses as a mistress of course!

“For months I’ve been trying to catch my husband screwing around and I can’t do it,” Calista complains in the promo video.

“Unless... you do catch him,” Joss replies with an idea. “We’re going to nail him!” And apparently Joss meant that literally. From what we’re shown in the trailer, Joss will seduce Luca while Calista captures the footage of her husband being unfaithful.

“You’re one twisted sister,” Calista responds to the devious plan.

Meanwhile, Harry (Brett Tucker) will embark on a mission himself as he tries to find a new gig. In the previous episode, Joss’ ex ended up in bed with the evil bartender Niko (Emmanuelle Vaugier) -- who shockingly revealed that she happens to be the girlfriend of the slimy Ellis (Kavan Smith), a partner in Wunderbar. But we're less concerned about Harry's new job and more worried what his night with Niko will mean for his crumbling relationship with Joss. Will the two ever get back together?

“Mistresses” will air Season 3, episode 7 on Thursday at 9 p.m. EDT on ABC.