What's the worst thing you've ever done? I don't mean skipping-church-because-you're-too-hungover bad. I mean having-an-affair bad. I mean walking-out-on-your-children bad. I mean opening-a-tube-of-green-Pringles-on-a-long-car-journey bad. Erin has four. Four unforgivable things. Four things that keep her up at night. The four worst things she's done, and she's about to confess them all. Strap yourself in.