Disarming""--that's the word; and if it didn't exist, it would have to be coined to describe this first novel (at age 75!) from actor-memoirist-playwright Emlyn Williams. His premise is less than promising: in 1935, the entire royal family (right down to the little prince who's 27th in succession) perishes when the dirigible ""Sky Whale"" explodes on its maiden voyage; and genealogical research reveals the new king to be an unaware, low-born (but legitimate) grandson of Edward VII's ne'er-do-well son Clarence--Jack Sandring from Cornwall, fledgling actor/stagehand in London musical comedy. Yet, with every neat touch and shrewd detail--from the eloquent title to the light-twist ending--Williams builds in so much sly comedy, devilish charm, and sheer warmth that his fantasy premise never has to bear too much real weight. Jack himself is the narrator here, and whether sketching in his bucolic background (""I hereby refrain from Memories of a Rustic Childhood"") or his cheerfully bisexual coming-of-age or his Coward-ish mÃ‰nage Ã trois with showfolks Kathy and Bruce, his tone is irresistibly straightforward: eager without being fatuous, ironic without being arch or jaded. So, somehow, you'll just about believe his story when, a few weeks after that royal catastrophe, he's hustled off to Buckingham Palace and informed that he's to be King John II. Numb at first, then determined to prove his mettle to doubting P.M. Stanley Baldwin (who says, ""I don't think he'll do""), Jack responds splendidly to the Pygmalion treatment from Willie Millingham, his sweetly helpful secretary/confidant: Jack's first radio speech to the nation (his own words rather than the stuffy ones ghost-written by the cabinet) is a triumph; his mum visits for tea and chats grandly about needlepoint with an 89-year-old princess; he survives a parade of potential queens, from mental defectives to elegant sex-and-drug fiends; all in all, he feels good enough to hum to himself ""You're the Top, You're the King of England. . . ."" But, throughout, he pines for commoner Kathy--who's now forever off-limits and won't even answer his letters. Even worse, kingship is full of major perils: someone's out to sabotage John II with vulgar stunts (a show-biz transvestite crashes the Royal Ball); and, soon bored with figurehead status, lack outrages most of Britain by demanding aid for Depression-ravaged Tyneside in words suggesting a reassertion of the Divine Right of Kings! Will Jack agree to abdicate? Will England become a republic? Will Kathy (and his tap-dance routines)come back to Jack? Worry not. It all sorts out splendidly--in a natty, naughty, surprisingly touching show that will entrance anyone with the slightest weakness for the Thirties, the theater, or the England that was and never will be again.