"Mistresses" returns for a fourth season and continues to focus on the scandalous lives of a sexy and sassy group of girlfriends, each on their own path to self-discovery. When it comes to love, these girlfriends find support and guidance with each other as they push the limits, test their boundaries and discover just how far they are prepared to go. They are willing to brave love's turbulent journey, as well as its excitement, secrecy and betrayal, all the while bound by the complex relationships they've created.
Harry's sister Kate surprise visits Harry and Joss, and exposes problems she is having with her fiancé. Meanwhile, Joss struggles with celebrating her engagement with Harry, and April gets an opportunity to apply for a painting fellowship.