She washed her hands when she came home. I mean, obsessively — three times in a row, up to her elbows, the way a surgeon washes. She'd never done that after "book club" in March or April, but by May and June she was doing it every time. She started leaving her phone face-down, even in front of me. She started wearing a perfume I'd never smelled before, cheaper and heavier than her usual, as if she'd put it on to cover something else. And then, one night in July, she came home and there was something in her hair. A long, single strand of something pale and fibrous, not a hair — more like a thread. Wool, maybe. Or fur. When I pulled it off her and held it up to the light, she looked at my hand like I was holding evidence. Then she laughed it off. "Oh — probably from the clinic." I nodded. But the clinic uses synthetic fibers on their beds, and I know because we went together once. I knew right then. And that's the night I decided I was going to find out what Riley did on Tuesdays, even if it meant crossing a line I couldn't come back from.