The film, produced by former silent film star Mary Pickford, stars Harpo Marx, Chico Marx, and, in a smaller role than usual, Groucho Marx, plus Ilona Massey, Vera-Ellen, Paul Valentine, Marion Hutton, Raymond Burr, Bruce Gordon (in his film debut), and Eric Blore, with a walk-on by then unknown Marilyn Monroe.
The plot was written by Frank Tashlin and Mac Benoff, based on a story by Harpo.
Private detective Sam Grunion (Groucho Marx) has been searching for the extremely valuable Royal Romanoff diamonds for eleven years, and his investigation leads him to a troupe of struggling performers, led by Mike Johnson (Paul Valentine), who are trying to put on a musical revue called Love Happy.
Grunion notes that the impoverished young dancers would starve were it not for the sweet, silent Harpo (Harpo Marx), at Herbert & Herbert, a gourmet food shop that also trafficks in stolen diamonds. Harpo kindly helps ladies with their shopping bags, all the while pilfering their groceries and stuffing them in the pockets of his long trench coat. When the elegant Madame Egelichi (Ilona Massey) arrives, store manager Lefty Throckmorton (Melville Cooper) tells her that "the sardines" have come in. Harpo sneaks into the basement and watches as Lefty lovingly unpacks a sardine can marked with a Maltese cross, and swipes the can from Lefty's pocket, replacing it with an unmarked one. Madame Egelichi, who has gone through eight husbands in three months in her quest for the Romanoff diamonds, is furious when Lefty produces the wrong can. When Lefty remembers seeing Harpo in the basement, she orders him to call the police and offer a $1,000 reward for his capture.
At the theater, meanwhile, unemployed entertainer Faustino the Great (Chico Marx) asks Mike for a job as a mind-reader, and when Faustino's clever improvisation stops the show's backer, Mr. Lyons (Leon Belasco), from repossessing the scenery, Mike gratefully hires him. Harpo, who is secretly in love with dancer Maggie Phillips (Vera-Ellen), Mike's girl friend, gives her the sardine can, and she says she will eat them tomorrow. A policeman sees Harpo inside the theater and brings him to Madame Egelichi, who turns Harpo over to her henchmen, Alphonse (Raymond Burr) and Hannibal (Bruce Gordon) Zoto. After three days of interrogation, Harpo still refuses to talk, and when he is left alone, he calls Faustino at the theater, using the bike horn he carries in his pocket to communicate. Madame Egelichi listens on the extension as Faustino declares that there are plenty of sardines at the theater, and she goes there at once.
Meanwhile, Mike has just finished telling the troupe that they do not have enough money to open when Madame Egelichi arrives and offers to finance the show. Mike cancels his plans to take Maggie out for her birthday so that he and his new backer can discuss the arrangements. In the alley outside the theater, Harpo, having escaped from Madame Egelichi's suite, finds the diamonds in the sardine can which had been set out for a cat, and puts them in his pocket. When he finds Maggie crying in her dressing room, Harpo takes her to Central Park, where he plays the harp for her and gives her the diamonds as a birthday gift.
On the opening night of the show, Grunion is visited by an agent of the Romanoff family, who threatens to kill him if he does not produce the diamonds in an hour. At the theater, Lefty and the Zoto brothers spy through a window as Maggie puts on the diamond necklace, but Mike asks her not to wear it, promising to buy her an engagement ring instead. As they kiss, Maggie removes the necklace and drops it on the piano strings. The curtain goes up, and when Harpo sees Lefty and the Zoto brothers menacing Maggie, he distracts them with a piece of costume jewelry and leads them up to the roof. Meanwhile, on stage, Faustino plays the piano, and when he strikes the keys forcefully, the diamond necklace flies into the air, drawing the attention of Madame Egelichi, who is watching from the audience. Faustino pockets the diamonds, then rushes to the roof to help Harpo. Madame Egelichi shows up with a gun and demands the necklace, but Faustino gives her the fake diamonds. After tying up Lefty and the Zotos and recovering the real diamonds, Harpo encounters Grunion, who has been hiding on the roof. Harpo drops the diamonds in Grunion's pocket, but then steals them back as Madame Egelichi begins to lead the detective away.
Later, in his office, Grunion comments that Harpo disappeared with the diamonds, never realizing their true value. Grunion interrupts his story to take a phone call from his wife, who turns out to be the former Madame Egelichi.Harpo Marx as Harpo
Chico Marx as Faustino the Great
Groucho Marx as Detective Sam Grunion
Vera-Ellen as Maggie Phillips
Ilona Massey as Madame Egelichi
Marion Hutton as Bunny Dolan
Paul Valentine as Mike Johnson
Raymond Burr as Alphonse Zoto
Bruce Gordon as Hannibal Zoto
Melville Cooper as Lefty Throckmorton
Leon Belasco as Mr. Lyons
Marilyn Monroe as Grunion's Client
Eric Blore as Mackinaw
The film has a musical score and lyrics by Ann Ronell, with a lively film noirish dancing version of Sadie Thompson featuring Vera-Ellen and former ballet dancer Paul Valentine as one of the United States Marines on a South Pacific Island.
Chico plays a duet on "Gypsy Love Song" with actor-musician Leon Belasco as Mr. Lyons, the owner of the stage props and costumes. Belasco, on violin, starts playing many fancy trills until Chico says, "Look, Mista Lyons, I know you wanna make a good impression — but please, don't play better than me!" Chico played this same tune in the Marx Bros. first film The Cocoanuts 20 years earlier, in 1929.
Love Happy was originally conceived as a solo vehicle for Harpo under the title Diamonds in the Sidewalk, but Groucho often said the brothers did the film to help Chico pay off gambling debts. Once Chico was in, the producers refused to finance it unless all three Marx Brothers were featured.
Groucho appears without his usual greasepaint moustache and eyebrows; by this point in his career, he had grown out an actual mustache for You Bet Your Life and no longer saw the greasepaint as dignified. He is rarely in the same scenes as his brothers (the three are never seen together), and mainly provides an encompassing narration to explain things in the film when the necessary sequences for a coherent narrative were unavailable. Groucho avoided mentioning the film at all in his autobiography, Groucho and Me (1959), apparently at that time considering A Night in Casablanca (1946) their last film together. He did acknowledge the film in his later book, The Groucho Phile: An Illustrated Life (1976). Because of the encapsulated nature of Groucho's scenes, it had long been assumed that his presence in the film was an afterthought. However, recently discovered letters from Groucho show that he was to have been part of the project from its earliest stages in 1946-47.
The production ran out of money during shooting, so a unique form of product placement (rare for the time) was featured in a rooftop chase around advertising billboards.
Although shooting began in August 1948, the film was not released generally until March 3, 1950. The film′s stated copyright is 1949, which is when it was shown in San Francisco on October 12. Originally released at 91 minutes, available non-theatrical prints run 85 minutes and contain some alternate footage with some brief snippets excised from some scenes and some gags completely eliminated. In 2015, Olive Films made the uncut 91 minute theatrical version available on DVD.
Love Happy is generally regarded by Marx fans and critics as the weakest Marx Brothers movie.
In its 8 October 1949 front page editorial, as well as its review of the movie in the same issue, the motion picture trade periodical Harrison's Reports, which always disapproved of any movie showing brand-name products, severely criticized this film for its rooftop chase among billboards promoting Baby Ruth, General Electric, Fisk Tires, Bulova watches, Kool cigarettes, Wheaties and Mobil.
At the end of his March 8, 1950 episode of his You Bet Your Life radio show, Groucho half-heartedly promotes the film as "Harpo, Chico, and I tell a few jokes and do some acting. It's very educational." In later years, on Today, Groucho dismissed it as a "terrible movie", while speaking of the lasting impression Marilyn Monroe made during her screen test.