Based on Leonard Wibberley’s novel, a tiny country in Europe has their economy ruined by a California wine and decides to go to war against the United States, hoping to win the peace. However, they manage to steal a new doomsday weapon and take a few prisoners.
In the tiny country of Fenwick in the Swiss Alps people speak English, and it is ruled by the Grand Duchess Gloriana XII (Peter Sellers) with help from Prime Minister Count Rupert of Mountjoy (Peter Sellers). Forest ranger Tully Bascombe (Peter Sellers) supervises the army of archers. The main export is a wine to the United States. In 1959 a California winery marketed a copy of this wine and took over its market share. Gloriana presides over a meeting in which Rupert tells them they are bankrupt. He says the only way out of their disaster is to declare war on the United States so that after losing the war they could win the peace. Gloriana asks if it is honest, and he admits it is not. Benter (Leo McKern) asks about their army, and Rupert says that Tully will lead them to New York where they will be arrested for not having visas. Rupert says the choice is disaster or prosperity, and they vote to declare war. Rupert signs the document and orders it mailed special delivery. He and Benter toast their defeat. Tully comes in and says he does not want to go to the war because it is the mating season in the forest. Rupert and Benter persuade him to go on the ocean voyage, but Tully says he gets seasick.
Tully asks the men of Fenwick if they love their country, and they say they will not enlist. Tully explains that they are at war with the United States, and they walk away. Gloriana appears as a band plays, and people cheer. Rupert tells the army that their cause is just, and he promises to pay their fare home if necessary. The army marches off to war.
Some 22 men change from their armor to modern suits. Tully gets a bus to stop, and they board a ship at Marseilles.
At the State Department in Washington an official opens the letter and reads the declaration of war, assuming it is a joke from the press.
The Fenwick army marches around the deck in their armor. Tully is seasick.
A New York newspaper reports the United States has the super-bomb and is conducting an air raid alert.
On the Queen Elizabeth the captain and his mate discuss this and that the United States has the new Q bomb which is greater than the H-bomb. The captain tells the small boat about the alert, and they shoot arrows at him.
Tully looks with binoculars and cannot see anyone in New York. A soldier explains to another that they are supposed to lose the war. The captain says it is peculiar there are no customs people. Tully tells them to have their passports and health certificates handy. A soldier hands him a guidebook to New York as the invasion manual.
The Fenwick army walks in the empty streets of New York. Will Buckley (William Hartnell) asks Tully why no one comes to capture them. Tully’s armor is squeaking, and Will identifies it and laughs. Tully gets gum on his shoe.
Inside people are dancing, and soldiers see them through a grate. Will shows Tully the newspaper about the air raid drill. Tully reads about the new bomb designed by Dr. Kokintz. Tully says they do not want to destroy their air raid drill, and he tells them where they can go to surrender.
At the New York Institute of Advance Physics the scientist Dr. Alfred Kokintz (David Kossoff) is working on the new bomb with his daughter Helen Kokintz (Jean Seberg). He tells her they do not know about his little working model. He says it can go off easily. A Civil Defense monitor comes in and orders them to leave. She tells him her father invented the Q-bomb. She says her father is going to disconnect it. She says it is the first working model. They say it could blow up all of North America. She hopes it is will never be used. She asks the man to bring them some sandwiches.
Two men get out of a Contamination Squad truck in air-tight suits. Tully and the army see the truck. The two squad men see them and think they must be from outer space. They run away, and arrows are shot at them. Tully tells them not to shoot. He says they need to surrender, and he says they will turn in the truck. They use the siren. The decontamination man tells the Civil Defense officials he saw men from Mars. The other man telephones that men from a flying saucer are there. The rumor spreads, and the numbers are exaggerated.
They get out of the truck and see the Physics building. Will says they should go back to the truck, but Tully leads them inside.
At the Pentagon the United States Secretary of Defense (Austin Willis) gets a call from General Snippet (MacDonald Parke) in New York about the rumors of men from outer space.
Helen tells her father they have to get to a shelter. Tully knocks and comes in with Will. Helen asks what they want. Tully says they came to capture Dr. Kokintz so that they can bargain their surrender better. Tully sees the Q-bomb, and Will suggests they take it with them. Dr. Kokintz tells Helen not to resist, and he warns Tully not to stumble because the bomb could destroy all of America. Tully fumbles it, but Will catches it.
Will carries the bomb, and the army goes to the truck. They see officers in a jeep, take cover, and shoot arrows at their tires. Tully takes General Snippet prisoner, but Snippet says Tully will be arrested. The soldiers take the general.
People are told by radio to stay where they are because they have been invaded by people from Mars.
Tully and the army return to the ship which sails.
The Secretary learns that they found Snippet’s jeep at the Physics building. They found a flag and arrows in the tires.
In Grand Fenwick at a meeting Rupert says they will let the Americans have their wine at a fair price. He says they want to get malted milk machines. He expects non-fraternization to last 48 hours, and then he wants the GIs to feel at home. Benter asks if they should have heard something by now.
On the ship Will makes General Snippet exercise with the others. Helen and her father are in a cabin and discuss how they can save the world by persuading them to let him dismantle the bomb. She agrees reluctantly and asks to see the dictator. Tully is seasick, knocks, and comes in. She complains about their cabin. She asks him to let her father dismantle the bomb as a personal favor to her. He says no. The ship moves, and he embraces her. She apologizes to him and asks him to forgive her. She says they can still be friends and asks if he likes American girls. He says he likes her, and she says he can kiss her. He feels seasick and goes out.
On the Queen Elizabeth the captain gets a warning about a pirate ship, and arrows are shot at them again.
Tully at Marseilles gets tickets for Fenwick. General Snippet complains that he was kidnapped.
The Defense Secretary talks to an officer about how the FBI found the declaration of war. The officer says they sent them some protests, but they ignored them. The Secretary says they got Dr. Kokintz and the Q-bomb and “practically control the world.”
People at Fenwick have signs welcoming the Americans. Gloriana, Rupert, and Benter are waiting for them with the crowd. The band plays an American march as the Fenwick army returns with their prisoners including four policemen. Tully explains that they won the war by capturing the Q-bomb. Dr. Kokintz warns that if the bomb explodes, it would destroy Europe. He asks permission to dismantle it, but Gloriana asks what he wants for breakfast. Helen says the bomb belongs to the United States, and they should give it back. General Snippet says he knows the Geneva Convention by heart, and Gloriana asks him to recite it some evening.
In a museum General Snippet and the policemen sees instruments of torture. Gloriana comes in and asks what he thinks of their exhibits. She explains they don’t use these things anymore. Snippet refuses to move unless food is served on tin plates. Gloriana calls in some attractive women, and the police go with them to a comfortable room and dine. The general eats in a cell off a tin plate.
Newspapers report that the United States was invaded. The BBC reports that the British have announced they will support Fenwick. The Soviet Union has stated they will work to see that the Q-bomb stays out of the hands of the imperialists.
Rupert receives a message and says it is from China. They offer to help them against the United States. Benter says they cannot do business with Red China, but Tully says it is from the other China.
The Secretary leads a meeting with military officers and persuades them they are stuck. He says Egypt wants the bomb and offers access to the Suez Canal. The Secretary says the Russians have offered twenty divisions. They want to send troops to help Fenwick, but the Secretary reminds them they are at war against Fenwick.
Rupert suggests they give the bomb back to the Americans, but Gloriana thinks they should wait. Rupert and Benter resign. Gloriana makes Tully prime minister. She is upset and goes out, but Tully says they won. Will says the world is no longer the same.
A general advises the Secretary to make peace with Fenwick, and he agrees to seek an armistice.
Rupert and Benter go to Helen who says she wants the bomb back with her father. They agree with her and offer to help her take the bomb home.
Tully is looking at the bomb in a prison cell.
Helen is taking a bath in a barrel. Tully knocks and comes in. She says she did not expect him for a half hour but then learns it is Tully. She says they can never be friends. She is hit by cold water and screams. He comes in, and she tells him to get out.
The Secretary arrives at the border of Fenwick and tells Will he came to discuss the surrender terms. Will says he will have to wait with the others. A Russian says they were all told to wait.
Rupert and Benter take the Q-bomb to General Snippet who carries it.
Gloriana plays the harpsichord and sings to Dr. Kokintz.
Helen says goodbye to Tully, and they argue over how the war was won by Fenwick. He says she is his prisoner and kisses her. She calls him a thief, and he goes out.
Rupert sends Benter to get the car and goes in to see Helen. He says her father is waiting with the others. Tully knocks, and she tells him to go away. He apologizes and says he loves her. He thinks she loves him too. She thinks he means it, but Rupert pulls her out the window.
The prisoners are sitting in a car, and Rupert and Helen arrive. She asks where her father is. She wants the bomb dismantled, but Rupert makes them leave.
An atomic bomb explosion is shown to the audience even though it is not part of the story.
The diplomats are playing a board game called Diplomacy.
In the car the general holds the bomb in his lap as the car backfires. He tells them to stop and fix the car.
Tully is caught with his foot in a trap, but he gets out and runs to the road where the car passes him. He runs after Helen and gets on a horse that won’t move. The car backfires and stops on a hill. The police get out to push the car, and then it rolls down the hill with no one driving. The car goes off the road and runs into a haystack by the diplomats. The police and Helen uncover the car and pull it out. The Q-bomb makes noise, and the general throws it to a policeman. They pass it around to the diplomats, and finally Tully gets it and puts it over a white line.
At a table Tully says he is ready and says the California wine must go out of business. He asks for $1 million, but the Secretary says they will probably get $1 billion. Tully says he and Helen are getting married. Tully says they want to keep the Q-bomb so that the big nations will disarm themselves. The Secretary asks if he thinks the big nations will agree to that. Tully says if they don’t, they will explode the bomb. Gloriana says Fenwick could be destroyed in any war. The Secretary leaves, and Dr. Kokintz gets Gloriana’s permission to examine the bomb to see if it is all right.
Dr. Kokintz drops the bomb and taps on it. He says the bomb was a dud all the time. Helen says she is proud of him, and Tully puts the bomb down. He says only they know. They go out, and Tully tells Will the bomb was never better.
This farce satirizes the cold war between the superpowers and the development of tremendously destructive weapons. How ridiculous these weapons are is shown when a tiny country with the most destructive bomb suddenly becomes powerful and can tell other nations what to do with the threat of destroying them if they do not cooperate. This is then turned against the big powers so that all these horrible weapons can be dismantled, making everyone safer and better off.