The cartoon later appeared (combined with two other Rocky and Mugsy cartoons) in The Looney Looney Looney Bugs Bunny Movie in 1981.
The cartoon opens with a pair of eyes looking through a peep door followed by the credits. The narrator explains how the Roaring 20's was a time of jazz, new fashion trends (such as oversized fur coats on men and short-skirted dresses, bell hats, knee socks, and long pearl necklaces on women), dance parties, and mobster violence. The scene then cuts to a pair of gangster cars shooting guns at each other (ceasing at a traffic light). One man, witnessing the gangster battles, hurries over to the nearest telephone booth and orders the operator to connect him to the police, but the dim witted operator takes so long to make the connection that the gangsters' gunfire shoots the telephone booth and man in half, to which the operator says "Sorry! You've been disconnected."
Over in Washington D.C., Bugs Bunny (addressed as Agent Elegant Mess in this cartoon) is assigned by his chief to infiltrate the gangster underworld in Chicago. As Bugs takes a taxi out to Chicago, he discovers that it's been compromised by Rocky and Mugsy.
At the hideout, Rocky and Mugsy have tied up Bugs and put his feet in a bucket of water, making it seem like he has a cold, but Mugsy pours in some cement. Both men then throw Bugs into Lake Michigan in the dark of the night, but Bugs manages to use a pipe as a snorkel and hop out of the lake.
The next night, the gangsters decide to throw a party to celebrate Rocky's birthday and the (supposed) death of Bugs. Rocky's guests include Jack "Legs" Rhinstone (wearing ladies' socks on his legs), "Baby Face Half" Nelson (whose face is the size of his cigar end), "Pizza Puss" Lasagna (whose face looks like the surface of a pizza), "Pistol Nose" Pringle (whose nose is shaped like a pistol, and breathes out cigarette smoke), and "Teeth" Malloy (whose giant teeth take up all of his face).
Mugsy announces Rocky's entertainment just as Bugs pops out of the cake, disguised as a flapper. During the entertainment, Mugsy, distracted by Bugs' disguise, nudges Rocky so he falls over, making Rocky punch him up the jaw. Just as Rocky comes up to Bugs to tell him he loves him, Bugs kicks Rocky up the jaw, making him drop his guns. The third kick has Rocky so deep under his hat that he has to feel the floor for his guns and fire aimlessly.
Once Bugs flees, Rocky sees he's been set up and orders all the gangsters in attendance to capture Bugs, but they fall to the floor dead (Rocky having shot them by accident). Just as Mugsy comments on Rocky making a boo-boo, Bugs comes in, disguised as a police inspector, and books Rocky for murder. Determined not to be booked, Rocky whips out a revolver. Bugs then whips out a carrot, which Rocky and Mugsy find funny, until the carrot end opens up and blasts them. When Bugs tries again, the carrot is empty, to which Bugs comments "That's the trouble with carrots! They're only good once!"
Rocky then retaliates with real gunfire and he and Mugsy chase Bugs across town into a factory. Unable to see in the dark, Rocky orders Mugsy to turn on the light, but once the light is on, Rocky see that Bugs has a gun aimed at him. He orders Mugsy to turn off the light, but Bugs blasts him before the lights go out. Rocky then orders Mugsy to switch places so that Mugsy will blast Bugs. After the places are switched and Rocky turns on the light, Mugsy fires, only to discover Bugs isn't there. By the time they turn around and see where Bugs is, Bugs blasts Rocky again and turns out the light.
Rocky and Mugsy then chase Bugs up a set of stairs into, what we think to be, a storeroom. Mugsy slams the door on Rocky, which prompts him to sock him up the jaw again. Bugs then escapes, locks the door, and runs down the stairs. A light then goes on revealing that the three characters are in the ACME Cereal Factory. Bugs then throws a switch, which send Rocky and Mugsy into a mixer and has them mixed about like "a merry go round at the amusement park." Bugs then throws another switch which puts them in the popper. When the cereals come out on the conveyor belts, Rocky has been placed into a "six pack" box and Mugsy has been placed into a "king sized" box (both boxes showing their pictures with "cut along dotted lines" on them).
The next day, with Rocky and Mugsy apprehended, Bugs takes them to Juliet Prison. Rocky and Mugsy are then sentenced by the court to spend twenty years of hard labor. As they're hammering away on the rocks, we see in the final shot that Bugs is joining them in the sentence, as the narrator explains that Bugs had lost the keys to the handcuffs.