Well, it's an Elvis movie.
Not that there's anything wrong with that, it's just that this isn't one of the better ones: the story slogs, the songs are (mostly) forgettable, the dialog's predictable, and "cynical drifter" is kind of a stretch for Elvis, artistically. He has the sneer already, but it's cute on his face, not in his voice.
Nevertheless, Charlie Rogers (Elvis) starts out as a lone wolf singer in a groovy teahouse, run by Jack Albertson. One night, a bunch of frat boys come in with their girlfriends (two of whom are uncredited Teri Garr and Raquel Welch) for beer and cokes. Charlie don't truck with no snobs, so he sings a song ("Poison Ivy League") to make his point, then loses his job for brawling with the boys out back.
After his waitress girlfriend bails him out of jail (like, right after), Charlie blows town on his comparatively wee motorcycle and heads for parts unknown. Somewhere in cow country, he sees a pretty girl, a crabby, hungover old man, and a stunningly beautiful woman in her late 50s riding in a Jeep. Charlie would like to pass this Jeep and flirt with the girl along the way, but the driver (the girl's father), refuses to let him pass, because you can't let hooligans take over the world or something. Eventually, Charlie is run off the road, his motorcycle wrecked and his guitar shattered.
The Jeep people turn out to be carnival folk: Joe Lean (Leif Erickson), his daughter Cathy (Joan Freeman), and the owner of the carnival, Maggie Morgan (Barbara Stanwyck). Maggie offers Charlie a job as a roustabout while he waits for his bike to get fixed, and he accepts, with every intention of hitting the road as soon as possible. If he can kiss a few girls along the way (Cathy in particular), all the better.
One afternoon, Charlie sings a song on the midway (as you do) and people start buying three throws for a dollar and candy apples and oh, just everything. Maggie decides to hire him as the opening act for the girlie show (it's called "Girlie Show" and one of the girls is uncredited Teri Garr...again) and Charlie becomes a local sensation. This is lucky, because Maggie's carnival is in a lot of financial trouble, thanks to an accident caused by Joe's drinking.
Joe doesn't like Charlie sniffing around Cathy, who in turn doesn't like Charlie sniffing around the fortune teller, Madame Mijanou (Sue Ane Langdon). The owner of a more profitable carnival (Pat Buttram) has also been sniffing around to see why Maggie's carnival has gotten so successful all of a sudden. He sees.
Just as Charlie starts to feel almost at home, a huge misunderstanding takes place involving a jackass patron, a missing wallet, and a mean drunk (Joe) that prompts Charlie to leave Maggie's show and join the humungous, Vegas-like carnival of her principal rival.
Obviously, everything works out: Charlie quits the bigger show that pays more and offers tons more exposure to help his friend Maggie and her crummy show that has the girl of his dreams and her mean, drunk father.
In other words: not Barbara Stanwyck's best vehicle, but if ever there were proof needed of her consummate professionalism, Roustabout is it. The part is dull and thankless, but she does it great. Behind the scenes, Elvis was properly deferential and sweet to her, taking Miss Stanwyck for a ride on his motorbike and listening to everything she said with the respect due an actor of her caliber.
It might be worth it to see 18-year-old Teri Garr do some high kicks in the Girlie Show...that's pretty cool; otherwise, you can watch the best number in the show right here, right now: