Fielding Mellish (a consumer products tester) becomes infatuated with Nancy (a political activist). He attends demonstrations and tries in other ways to convince her that he is worthy of her love, but Nancy wants someone with greater leadership potential. Fielding runs off to San Marcos where he joins the rebels and eventually becomes President of the country. While on a trip to the states, he meets Nancy again and she falls for him now that he is a political leader.
In the Republic of San Marcos, in Latin America, the president is murdered in a Coup d'État promoted by General Emilio M. Vargas. In New York, the products tester Fielding Mellish meets the political activist Nancy and they have a love affair. Fielding has an unrequited love with Nancy, who believes that he is immature and without leadership. Fielding decides to travel to San Marcos and General Vargas plots a scheme the assassination of Fielding to be supported by the USA against the rebels led by Esposito. However the rebels save Fielding and train him in guerrilla warfare. General Vargas flees to the United States. Esposito deranges with the power and Fielding becomes the President of San Marcos. He wears a long beard and travels to USA seeking financial support to the country and he meets Nancy again, who falls in love with him.
Nebbish Fielding Mellish works as a product tester for a large corporation in New York. His relationship with Nancy, a social activist, is the first he's had in quite some time. So when Nancy breaks up with him - she knowing something is missing, but not being able to put her finger on what that is - Fielding believes the way to win her back is to get into activism, most specifically to move to the Latin American republic of San Marcos, where the elected president was assassinated and replaced by General Emilio M. Vargas, a military dictator. Nancy first met Fielding in trying to get signatures on a petition for the US to break all ties with the military government. Being an American, Fielding ends up being used as a pawn between Vargas and the revolutionary forces, led by Esposito, that function of pawn which may have fatal consequences for him. The question becomes if he is able to survive whether his actions in San Marcos will produce his desired end goal of getting Nancy back.
When a bumbling New Yorker is dumped by his activist girlfriend, he travels to a tiny Latin American nation and becomes involved in its latest rebellion.
- On the Wide World of Sports television broadcast, American sportscasters Don Dunphy and Howard Cosell (playing himself), report that the president of the island Republic of San Marcos has been assassinated and replaced by a dictator, General Emilio M. Vargas (Carlos Montalbán).
Meanwhile in New York City, clumsy looser Fielding Mellish ((Woody Allen)) works as a product researcher at General Equipment, where he tests electrically warmed toilet seats, coffins with piped-in music and the new "Execusizer," a gym built into the desks of busy corporate heads. Unhappy with his job, Fielding blames his lack of success on the fact that he never finished college.
Fielding has also been unsuccessful in his attempts to date women, until Nancy (Louise Lasser), a politically active college student, knocks on his door, asking him to sign a petition urging the United States to support the revolutionaries in San Marcos, who are rebelling against the new corrupt dictator. Although Nancy is busy with yoga classes and her women's group, Fielding talks her into going out with him. Smitten, he accompanies her to political rallies and riots, and eventually makes love to her.
Fielding's newfound happiness is shattered when Nancy, feeling that "something is missing," breaks up with him. She explains that she needs someone who is a leader, more politically aware, and less emotionally, sexually and intellectually immature. The breakup depresses Fielding so much that he quits his job and decides to go to San Marcos, where he and Nancy had planned to vacation. Before leaving, he visits his parents, a surgeon and nurse who are in the middle of operating on a patient, to explain that he will be gone for a while. Disappointed that Fielding has not followed him into the family business, Dr. Mellish tries to give him confidence by insisting that he take over the operation, but his mother gives him her blessing.
In impoverished San Marcos, where each peasant has been ordered to pay the dictator his weight in manure, a captured rebel is tortured by being forced to listen to a recording of Naughty Marietta , which prompts him to confess that the rebels are planning a revolution on July 4th. After Fielding checks into a hotel, he receives an invitation to dine with Vargas at the palace.
During the meal, Vargas explains to Fielding that he wants to keep his people safe from Communism by exterminating "a few troublemakers." Vargas ignores Fielding's point that the rebels are not Communists and sticks Fielding with the bill. After Fielding leaves, Vargas and his men decide that Fielding is "perfect" for their plans. Later, Vargas' men, who are disguised as rebels, try to kill Fielding, intending to blame the death of an American citizen on the revolutionaries in order to win United States support for their regime. Fielding escapes, but is then captured by the real rebels, who take him to their leader, Esposito.
At the rebels' camp, Fielding is told that Vargas has already reported his death to the newspapers and will kill him to prevent the truth from getting out. The rebels want him to stay and risk his life for their cause, but Fielding believes that being dead is "a tremendous drawback" to one's sex life and prefers to remain cowardly. However, he trains with the rebels and learns about guns, grenades, camouflage and first aid. When the camp is low on food, Fielding is sent to raid the town and, with a few other men, enters a café and orders a couple thousand sandwiches, wheelbarrows of cole slaw and some drinks, then has it delivered.
Esposito later sends Fielding and two rebels to kidnap the British ambassador to hold as a hostage until imprisoned sympathizers are freed. While sedating the ambassador with sodium pentothal, Fielding accidentally renders his comrades unconscious. When the ambassador escapes, his revived co-workers flee and Fielding grabs a cross and joins a Catholic procession in order to evade some suspicious soldiers.
Meanwhile, mistaking the United Jewish Appeal for the CIA, Vargas makes a pact with them for support, and when the rebels attack, he discovers that the Jewish fundraisers offer little protection. Although the CIA does send men, half the agents are sent to fight for the dictator and the other half to fight against him. His regime defeated, Vargas flees to the safety of Miami.
After the rebels' victory, Esposito announces that he is the ruler of San Marcos, and orders that the country's official language will be Swedish and that citizens must now change their underwear every half hour, wearing it outside their clothing so that it can easily be checked. These proclamations and others cause the rebels to realize that power has driven Esposito mad. At the request of his comrades, Fielding takes over as president, but it is soon apparent that San Marcos needs the support of other countries in order to prevent future corrupt dictators from seizing control. The problem, Fielding and his close associates realize, is that Americans think of them as Communists, and Communists believe them to be American puppets. In addition, they have nothing to barter for aid, except bananas. Fielding's advisers urge him to go to the United States and raise money, but he knows that, back home, his reputation as an uneducated product tester has no clout.
Disguised in a red beard and mustache, Fielding flies to the United States, where he is officially welcomed as San Marcos' leader. There Fielding's interpreter translates by repeating every English sentence in heavily accented English, until men in white coats with a butterfly net arrive to take him away. During a dinner fundraiser at which he is the speaker, Fielding tries to tell a joke about a farmer who has an incestuous relationship with both his daughters, but decides he is telling it to the wrong crowd. Nancy, who does not recognize him, approaches to express her admiration for the leader and, after they go to bed together, Fielding reveals his true identity, after which Nancy remarks that she now knows why something in their sexual encounter seemed to be missing.
Meanwhile, the FBI sees through Fielding's disguise and, based on his record of involvement in riots and protests, assumes that he is trying to subvert the government. On the six o'clock news, newscaster Roger Grimsby reports that Fielding has been charged with being a subversive impostor. At his trial for charges of fraud, inciting a riot, conspiracy to overthrow the government and using the word "thighs" in mixed company, Fielding acts as his own lawyer. Both J. Edgar Hoover, who comes to court (disguised as a black woman), and Miss America provide testimony against Fielding. Although an acquaintance describes Fielding as a "warm, wonderful human being," the court reporter types that he is a "conniving little rat." While the jury passes around a joint, Fielding, acting as both lawyer and defendant, attempts to cross-examine himself, causing the judge to order him bound and gagged. Fielding is found guilty on twelve counts and sentenced to 15 years, but the time is suspended if he promises not to move into the judge's neighborhood.
A free man, Fielding proposes to Nancy, and their wedding night at the Royal Manhattan Hotel is covered by Dunphy and Cosell for Wide World of Sports . From their spectator-filled hotel suite, Cosell provides a play-by-play description of the action. In an interview with Cosell after the consummation of their marriage, Nancy states that Fielding was not the best she has had, but also not the worst, and Fielding predicts that their next "bout" will occur in late spring. Cosell wraps up the interview by saying that "they may live happily ever after and again they may not," but promises to be there to cover the action.