The Manual on the Shelf

Margaret Chen kept her Red Cross first aid manual on the kitchen shelf between a cookbook and a potted basil plant. She had taken the certification course twice, scored perfectly both times, and could recite the steps of CPR the way some people recite the Lord's Prayer — fluently, automatically, without thinking. On a Tuesday evening in March, at a crowded diner on Elm Street in downtown Asheville, a man three booths away clutched his chest and slumped forward.…