RKO's third Fred Astaire-Ginger Rogers film, Roberta is an excellent adaptation of the 1933 Jerome Kern & Otto Harbach musical of the same name, which was itself based on Alice Duer Miller's 1933 novel Gowns By Roberta, including the musical's best songs ("Yesterdays", "Smoke Gets In Your Eyes", "Let's Begin", and "I'll Be Hard To Handle") and adding two even better songs of its own ("I Won't Dance", which was reused from Kern's failed 1934 musical Three Sisters and given new lyrics by Dorothy Fields, jimmy McHugh and Otto Harbach, and "Lovely To Look At", with lyrics by Fields and music by Kern and McHugh).
Astaire and Rogers are, in fact, secondary characters in the film -- a bandleader from Indiana (Huck Haines) and an old friend from back home, Lizzie Gatz, who is posing as a fake Polish countess named Scharwenka in Paris, where Haines and his Indianans have travelled to Paris for a nightclub gig. The leads are Randolph Scott as a former star Harvard football player John Kent who has tagged along with the Indianans for a lark, and Irene Dunne, who is his Aunt Minnie's partner Stephanie in a fashionable Parisian dress shop ("Gowns By Roberta")...and is, incidentally, a princess. Things get complicated first by The Indianans losing their gig because they aren't really "indians", which the club owner was expecting, and Aunt Minnie dying without a will, leaving her half of the dress shop to Kent, who has fallen in love with Stephanie. This would be fine, except Kent's stuck-up estranged girlfriend shows up and tries to get him back because he's now rich. All ends well, of course. And there's LOTS of great Astaire-Rogers dancing to go along with those fabulous songs.