In 1960, for the first time since the Best Novel Award's inception, none of the nominees were American: both Philip MacDonald and winner Celia Fremlin hailed from the United Kindgom. While The Hours Before Dawn was very much a 50's book, it was a fit prelude to a decade marked by a British Invasion even more ferocious as the one striking pop music around the same time; it was also the last bow of a genre - psychological suspense - which had been dominating the mystery field for the last ten years.
Except for Charlotte Jay's inaugural win, the Edgar in the Fifties was largely what it has sadly become again over the last decade: a local award for local writers. Only three foreign writers achieved a nomination between 1956, the first year for which we have a list of nominees, and 1959. This makes the 1960-67 British takeover all the more impressive, though not that surprising. The Sixties were not exactly American mystery writing's brightest hour, and natives didn't fare much better abroad as a quick glance at the other two major awards of the time, Britain's Gold Dagger and France's usually americophile Grand Prix de Littérature Policière, shows. The British on the other hand experienced a spectacular ressurection after a period of relative lethargy and suddenly sounded "edgier" to both readers and critics than their colleagues from across the pond. Donald E. Westlake's win in 1968, nine years after Stanley Ellin, may have sounded like a restoration confirmed the following year by the crowning of Jeffery Hudson/Michael Crichton. This restoration, however, didn't last as another three years of foreign occupation followed, culminating with the unprecedented (and, to this day, unique) victory of a translated book.
Whatever may be, voters seem to have drifted away from their earlier commitment to "progressive" mystery writing - only a few of the decade's laureates can be said to "push the envelope" and bring something new - in favor of a greater eclectism: police procedurals (J.J. Marric's Gideon's Fire, Nicholas Freeling's King of the Rainy Country) spy novels (John Le Carré's The Spy Who Came in From the Cold, Adam Hall's Quiller Memorandum) thrillers (Crichton's A Case of Need, Dick Francis' Forfeit) a mystery comedy (Westlake's God Save the Mark) a caper (Eric Ambler's The Light of Day) an ambitious crime novel (Julian Symons' The Progress of a Crime) and finally, incroyable mais vrai, a whodunit (Ellis Peters' Death and the Joyful Woman) That Ira Levin's Rosemary's Baby could find its way to a nomination is further proof that ideas about what constitutes an Edgar-worthy novel had significantly loosened over the decade.
All this came at the expense of the ruling class of the previous decade: Ross MacDonald's unfruitful three nominations marked the beginning of a long eclipse of the P.I. novel while psychological suspense went the way of dinosaurs - a demise most certainly hastened by the progressive marginalization of female writers. Only in the Eighties and the Nineties would some equilibrium be (temporarily) achieved again but that's another story.