The Season 4 premiere of “Mistresses” ended on a high note, but it looks like things will take a dark turn in episode 2 when Harry’s sister makes the trek from Australia to California.

According to the synopsis for the forthcoming installment, titled “Mistaken Identity,” Harry’s (Brett Tucker) sister Kate (Tabrett Bethell) will stir up trouble when she learns her brother has asked Joss (Jes Macallan) to marry him. In episode 1 of the hit ABC series, Harry popped the question to Joss, which she accepted with an enormous smile. But Joss and Harry’s massive grins will fade when Kate points out an obvious flaw in their relationship.

“Mistresses” Season 4 Spoilers Kate (Tabrett Bethell, left) will cause trouble for Joss (Jes Macallan) in Season 4, episode 2 of “Mistresses.” Photo: ABC

“Marrying your ex-sister-in-law? There’s nothing normal about that,” Kate says to the couple during what appears to be their engagement party. “You really think everyone is going to celebrate this?”

And apparently Kate isn’t the only one who feels that Joss and Harry’s relationship is odd. In the promo video for episode 2, Joss asks her close friends, April (Rochelle Aytes) and Karen (Yunjin Kim), if it’s strange that she’s marrying her former brother-in-law. They respond with a long silence.

“What are we doing?” Joss asks, as she begins to question her relationship with Harry.

While Joss struggles to celebrate her engagement, April will get an exciting opportunity to apply for a painting fellowship, and Marc (Rob Mayes) follows his dream by joining a band. Karen, however, will be faced with new obstacles after her erotic novel gives her the title “sexpert.”

“Mistresses” airs Mondays at 10 p.m. EDT on ABC.