It was supposed to save us. It destroyed us.

My husband, Marcus, and I used to be so in love. But now, after ten years together, we barely talk. I've seen so many of our friends marriages end in divorce, and I'm prepared to do whatever it takes to stop that from happening to us.

And then I meet Erin. She tells me all about her perfect marriage to Kieran, and I'm shocked when she reveals the secret to their marital bliss they have an open marriage. My heart starts to race as I consider it for me and Marcus. Could we really do this?

When Marcus cautiously agrees, I know it can't be with strangers, and so I call Erin. She tells me there is only one rule: complete honesty. But when I meet Kieran, it doesn't take long for me to break that rule. Soon this isn't an open marriage, but an affair.

As I start to fall for Kieran, Marcus becomes the attentive husband I've been craving, and I'm soon full of regret. This was all an awful mistake and I swear to end it. But my blood runs cold when Erin is reported missing. Who is this couple I've entangled our life with? And as the police knock on my door, it's much more than just my marriage that is now at stake.

For fans of Lisa Jewell, Gone Girl and The Housemaid, this is a psychological thriller with a twist you'll never see coming.