Katie, Trudi, Siobhan, and Jessica are four thirty-something women who've been good friends since college. Their lives have taken very different turns, but they all have one thing in common - infidelity. Their tangled web of love and deceit envelops all four woman with life-changing results.

Katie (played by Viva Blackpool's Sarah Parish), the group's emotional rock, is a well-respected doctor. She's been having an affair with a terminally ill patient for the last two years and crosses even further professional boundaries when he asks her to make a huge sacrifice.

Trudi (About a Boy's Sharon Small) is a 9/11 widow, unable to achieve closure as the body of her husband, Paul, was never found. She is trying to bring up their two daughters on her own, while struggling with her desire to move on with her life. Following several years of no sex, Trudi begins a string of awkward dates with handsome, single dad Richard (The Office's Patrick Baladi).

Siobhan (Nip/Tuck's Orla Brady) seems to be living in wedded bliss with husband, Hari (Raza Jaffrey, MI-5), and she has a successful career as a lawyer. The only problem is that Hari desperately wants to be a father, and their sex life has become less about "making love" and more about "making babies". However, she discovers red-hot passion with her flirtatious colleague, Dominic (Adam Rayner).

Jessica (Shelley Conn from Charlie and the Chocolate Factory) is a fun-loving commitment-phobe whose insatiable sexual appetite makes her irresistible to men and a mistress to many, including her boss, Simon (Adam Astill). Her commitment to her friends is unshakable, but marriage is the last thing on her "to do" list in life - an irony that is not lost on her when Simon asks her to organize the perfect wedding for lesbian couple Lisa (Alys Thomas) and Alex (Fringe star Anna Torv).

As life and love take them from excitement and happiness to torment and loneliness, the friends are simply struggling to hold it all together.