In the early morning of 6 April 1941 in Belgrade, the capital of the Kingdom of Yugoslavia, two roguish bon vivants Petar Popara, nicknamed Crni (Blacky) and Marko Dren are heading home. They pass through Kalemegdan and shout salutes to Marko’s brother Ivan, an animal keeper in the Belgrade Zoo. Marko lets Blacky’s pregnant wife Vera know that they enrolled Blacky in the Communist Party (KPJ).
Later, the hungover Blacky is eating breakfast while pregnant Vera complains about his supposed affair with a theatre actress. Suddenly, the roar of the planes is heard, and German bombs begin falling on Belgrade. After the air raid is over, Blacky goes out against the wishes of his wife and inspects the devastated city. Encountering building ruins and escaped wild animals from the zoo, he also runs into disconsolate Ivan carrying a baby chimp named Soni. The Royal Yugoslav Army’s resistance is quickly broken, and German troops soon occupy and dismember the entire Kingdom. Blacky starts operating clandestinely as a communist activist along with Marko and others. Blacky occasionally visits his mistress Natalija Zovkov who has been assigned to a special actors’ labour brigade that is helping the city’s rebuilding effort under German occupational control. An acclaimed, pampered, and celebrated actress in the National Theatre, Natalija has caught the eye of a high-ranking German officer named Franz.
Marko has set up weapons storage and hideaway spot in the cellar of his grandfather’s house. Following their interception of a large trainload of weapons, Marko and Blacky are identified as dangerous bandits in German radio bulletins. While Blacky is off hiding in the woods as Germans are intensifying door-to-door raids in the city, Marko takes Vera, Ivan and many others into the cellar to hide. Vera is due and gives birth to a baby boy, who she names Jovan before dying.
In 1944, and Blacky is in town to celebrate his son’s birthday at a local communist hangout. The two best friends head for the theatre in a jovial mood. They see Natalija performing on stage in front of Franz and other German officers, and Blacky shoots Franz in the chest. With Natalija, Blacky manages to reach the river boat anchored just outside Belgrade. Naturally, Marko is along as well, and all are getting ready for a forced wedding despite Natalija’s protestations.
The party is interrupted by German soldiers surrounding the anchored boat. Suddenly, Franz is seen yelling, demanding Blacky and Marko release Natalija, who runs to Franz. Blacky is captured by Germans and tortured in the city hospital with electric shocks while Franz and Natalija visit her brother Bata at the same hospital. Meanwhile, Marko has found a way to enter the building through an underground sewer passage. Sneaking up on Franz, Marko strangles him to death with a cord in front of Natalija who switches sides once again. Marko then proceeds to free Blacky. They leave with fatigued Blacky hidden in a suitcase, but Blacky is injured by a grenade.
A few days later on Easter 1944, Marko and Natalija, now a couple, are watching a comatose Blacky. In late October, the Red Army accompanied by Yugoslav Partisans enters Belgrade. Marko gives fiery speeches from the National Theater balcony during the Trieste crisis, socializes with Josip Broz Tito, Ranković and Edvard Kardelj and he stands next to Tito during military parades through downtown Belgrade.
In 1961, Marko is one of Tito’s closest associates and advisors. The physically recovered Blacky and company are still in the cellar under the impression that the War is still going on above. Marko and Natalija attend a ceremony to open a cultural center and unveil a statue of Petar Popara Blacky, who everyone thinks died, becoming a People’s Hero. With the help of his grandfather who is in on the devious con, Marko oversees the weapons manufacturing and even controls time by adding hours to a day so the people in the cellar think that only 15 years passed since the beginning of World War II instead of 20. They’re continuously making weapons, and Marko profits from it enormously.
The filming of an epic state-sponsored motion picture based on Marko’s memoirs titled Proleće stiže na belom konju (Spring Comes On A White Horse) begins above ground. Soon, Blacky’s 20-year-old son Jovan will marry Jelena, a girl he grew up with in the cellar. Marko and Natalija are naturally invited for a celebration. Ivan’s chimpanzee Soni has wandered into a tank and fires a round blowing a hole in the wall. Soni wanders off, and Ivan follows.
Blacky, with his son Jovan, emerges from underground for the first time in decades. They encounter the set of Spring Comes On A White Horse and believing the war is still on, kill two extras and the actor playing Franz. In the manhunt, Jovan drowns but Blacky escapes.
In 1992 at the height of the Yugoslav Wars, Ivan re-emerges with Soni, whom he was recently reunited with. He stumbles upon Marko, who is attempting to broker an arms deal in the middle of a conflict zone. The deal falls through and Ivan catches up with and Marko beats him to unconsciousness, then commits suicide. Natalija arrives and rushes to Marko’s side, proclaiming her love for him. They are captured by militants and they are ordered to be executed as arms dealers by militants’ commander, Blacky.
Blacky moves his people out to the cellar that he lived years ago, taking Soni with him. He sees an image of Jovan in a well, and inadvertently falls in while reaching for him.
In a dreamlike ending sequence, Blacky, Marco, and others are reunited at an outside dinner party, celebrating Jovan’s wedding. Ivan gives a few parting words, ending with “Once upon a time, there was a country.”