What will we do when there are no longer caches of letters to piece together and decipher; only vague memories of myriad emails? We will be like butterfly hunters flailing around with our nets, hoping to catch some rare specimen with glittering wings among the detritus of daily exchanges. The letters of Ida Nettleship, first wife of the arch-bohemian Augustus John, are a case in point: gathered together here from diverse sources by her granddaughter Rebecca John and expertly introduced by John’s biographer Michael Holroyd, they constitute a rare epistolary treasure trove.