Stewart O’ Nan’s fiction has always paid close attention to the people and relationships that shape us. In his new novel “Evensong” he brings that attention to bear on a vivid cast orbiting Emily Maxwell as she enters her 90s. This is the concluding chapter in a trilogy that began with “Wish You Were Here” and continued in “Emily Alone” and it widens the lens to explore not only Emily’s interior life but the network of care surrounding her.