Birdlike, darling Letty Montressor (Darcy's latest virginal but headstrong Regency belle) is clumsily running away from an arranged marriage when she literally bumps into Harry Tyne--rakish, disowned great-nephew of rich Lord Aubrey. And when it turns out that poor orphan Letty has ""a voice that would make a fortune if I were not too genteelly bred to think of performing in public,"" Harry and the Baron (a suavely elderly Charles Boyer type) whisk Letty off to Vienna to be the singing star of their new gambling salon. Letty is carefully coached and chaperoned, of course, but she falls in love with Harry tout de suite; alas, he treats her like a child and is himself, malheureusement, decorously shacking up with Lady Hester Luddington. So Letty tries to make him jealous--by agreeing to marry slimy, dashing Count Radoczy (Harry rescues her in the nick of time from the Count's phony marriage/seduction scheme). And she tries to make Harry grateful--by conspiring with her singing-master to get hold of evidence that Harry, who's been scorned by his great-uncle ever since being caught cheating at cards, was framed by bis evil Uncle Marius. Harry, however, is too proud to use this evidence; only after Marius (also in Vienna) repeatedly tries to kill him does he reconcile with old Lord Aubrey. And only after all have returned to England does Letty finally get fed up and run away (mistakenly believing that Harry's about to wed Lady Hester). Harry comes to his senses then, of course, just like Louis Jourdan did at the end of Gigi. Everything that happens here, in fact, is awfully familiar, even Barbara Cartland-ish; and Darcy's humorous touches aren't as strong or successful as they've been in the past. Still, it's all as light and painless and franÃ‡aise as always, and Vienna (without, thank Heavens, guest appearances by Franz Schubert, et al.) will make a nice change of ton for Darcy's many fans.