“Evensong” by Stewart O’Nan is a moving and deeply observant novel set in Pittsburgh, Pennsylvania, that captures the quiet complexities of marriage, memory, faith, and aging. Pittsburgh’s Humpty Dumpty Club, an organization of elderly women who support one another and their spouses through their golden years, finds itself in shambles after their leader, Joan, injures herself and can no longer manage the group. Determined to keep the organization running, Joan appoints Kitzi as the group’s new leader.