I’m twenty-four, newly separated, living temporarily in my mother’s house after my marriage collapsed. My mother has just remarried a rich, cold, older man—Gabriel—who is everything my soft ex-husband wasn’t.

* * *

The key turns in the lock at 11:47 p.m. and the sound goes straight between my legs.

I am sitting on the edge of the guest-room bed in the dark, still wearing the thin cotton nightgown my mother bought me “for comfort.” It barely covers the tops of my thighs. I have been listening to the house for two hours—the low murmur of their voices downstairs, the clink of ice in glasses, the occasional soft laugh that...