In 'Mercy Street,' Jennifer Haigh mines memories of volunteering at a clinic that provided...

It’s hard to know, ever, where a story begins. We touch down in a world fully inhabited by others, a drama already in progress. By the time we make our entrance—incontinent and screaming, like dirty bombs detonating—the climax is a distant memory. Our arrival is not the beginning; it is a consequence.

The starting point is arbitrary. When Claudia looks back on that winter (as New Englanders can’t help doing), the days fuse together in her memory: the weak light fading early, salt trucks clattering down the avenues, a bitter wind slicing through her coat. She had no sense, at the time, of forces aligning, a chain of events set into motion.

Like everyone else, she was distracted by the snow.