“Thank you,” I say sweetly when she tells me I’m lucky to have such a beautiful family. But I want to tell her it’s not just luck. A family is like a fortress you have to defend all the time. You can’t relax because there’s always someone looking for a breach, always someone trying to get in. Someone just like her…

When I arrive unannounced at my husband’s studio in need of a shoulder to cry on after hearing that my best student, Alex, has died, I see a pair of wineglasses drying by the sink and my deepest fear is confirmed: my husband is having an affair.

Most women would fall to their knees in tears and throw him out of the house—but I just can’t bring myself to do it.

Instead, I go home and cook a healthy dinner for our children, walk the dog and unload the dishwasher without complaint. I will make him see that I’m still the woman he married; attractive, successful, the glue that holds our perfect family together. I need this marriage to work to protect a terrible secret of my own, something that would destroy everything I’ve already sacrificed so much for.

But when the police arrive at my door asking questions about Alex’s death that I can’t answer, and threatening text messages start appearing on my phone, I know that someone close has been watching me very carefully.

The truth is, there are three people in my marriage, but only one of them is deadly…