The film opens with long, beautiful shots of ancient European art and sculptures being blown to pieces amidst the sounds of war and dissonant screams; a lone narrator begins his tale of "eight American soldiers" as the scene abruptly flashes back to a few weeks earlier.
Prior to the Battle of the Bulge, a ragtag squad of American soldiers (implied to be some sort of replacement outfit), led by one-eyed Major Abraham Falconer (Burt Lancaster) and including Sgt. Rossi (Peter Falk), art expert Captain Beckman (Patrick O'Neal), and the highly intelligent narrator and sole African-American, Pvt. Allistair Benjamin (Al Freeman Jr.), take shelter in an ancient Belgian castle, the Maldorais, containing many priceless and irreplaceable art treasures. Although Falconer begins an affair with the young and beautiful Countess (Astrid Heeren), he is surprised to find the Count of Maldorais Henri Tixier (Jean-Pierre Aumont) encouraging him; in fact, the impotent nobleman hopes the Major will impregnate the Countess so that his line may continue. Meanwhile, Beckman begins to butt heads with Falconer over both the value of the art (in the context of either saving or destroying it in the event of a German assault) as well as Beckman's own unrequited attraction to the Countess, who seems to symbolize the beauty and majesty of the European art that he had studied before the war. The enlisted men seek their own pleasures in the brothel of the nearby town, the psychedelic "Reine Rouge" (Red Queen) run by a mystical madam, while Beckman marvels at the castle's artworks, many of which are stored beneath the castle for safekeeping. Sgt. Rossi, a baker before the war, falls in love with a baker's widow and decides to go AWOL, resuming his pre-war life. Others in the group are sympathetic to his cause, and rather than arresting him, try and talk him into re-enlisting. Another soldier falls in love with a Volkswagen Beetle; his affection for the foreign vehicle borders on paraphilia and becomes a long running and anachronistic gag throughout the rest of the movie.
Soon after the very first scene, that of the ragtag group, slowly riding on a problematic Jeep, there is a sense of foreboding, a feeling of inevitability of what will eventually transpire. But in the mean time, the soldiers' days of leisure and peace almost threaten to undermine the very reality and the ugliness of the war itself. There is a recurring theme of eternal recurrence, as one soldier drunkenly ponders out loud that maybe he's "been here before". And, although the men are eager to sit out the war that they feel will soon end, the audience is not so sure. The experienced Major Falconer confirms the audience suspicions, by predicting that Germans will attack the thin American positions in the Ardennes and that the castle is a strategic point in the Germans advance towards the crossroads of Bastogne. The Major's theories are further confirmed when he sees German star shell signals and successfully ambushes a German reconnaissance patrol led by a German officer who was once billeted in the castle and was a previous lover of the Countess.
Captain Beckman and the Count are horrified that the Major will not abandon the castle, a decision that will surely lead to its destruction; Falconer, however, is adamant that to give the Germans one thing means that they'll just end up "taking everything" later on (see appeasement). Falconer prepares defensive positions around the castle and sends his unit into town. The Germans are initially taken by surprise, as Falconer directs the local sex workers at the "Reine Rouge" to draw them into a trap with Molotov cocktails; however, the defenders soon find themselves outnumbered and outgunned (although two GIs manage to steal and repurpose a working German tank, which they jokingly claim is "better than ours"). Seeing no other choice but to retreat to the safety of the castle, Falconer attempts to rally shell shocked American troops retreating from the Ardennes into the Maldorais, forcing (at gunpoint) a band of zealous, hymn-singing conscientious objectors, led by Lt. Billy Byron Bix (Bruce Dern), to lead the dazed survivors in a bizarre Pied Piper-esque procession; symbolically, they are all mostly killed by an exploding shell, all except for Falconer, who stoically returns to the castle for his last stand astride a pale white horse. He returns to find that the Count has run over to the German lines; Beckman thinks he has a scheme to betray them and let the Germans seize the castle by using the underground storage tunnels to gain access; however, it is soon revealed that the Count was really only trying to buy as much time for the Americans as possible so that they could make it to the castle and strengthen their defenses. As soon as his ruse is discovered, he is gunned down trying to run from the Germans. Falconer and Beckman put aside their personal and ideological differences and grimly prepare for the oncoming assault with a .50 caliber machine gun pointed across the castle grounds.
At the conclusion of the film, everyone defending the castle, (with the exception of Pvt. Benjamin and a pregnant Countess, who escape to safety using the art storage tunnels following the orders of Maj. Falconer) is eventually killed by waves of besieging Germans. The final battle scene is bizarre, featuring the enemy storming the gates of the castle using a ladder carrying fire truck, as much of the castle (along with its art treasures) is obliterated by artillery, incendiaries and other weapons. Part of the ending is brilliantly overdubbed by the narrator who explains (which is how Pvt. Benjamin's book will eventually read) how all the Americans survive, when in fact we can clearly see on the screen that all the Americans (except Pvt. Benjamin) die.
Maj. Falconer, the last defender left alive, begins to think of all of the people whom he has killed or have died because of his actions as well as the Countess as he guns down the rapidly approaching swarm of German soldiers, implying that he did indeed feel guilty about their deaths and that he loved the Countess much more than he let on. A shell finally lands on top of his position and explodes as the screen goes white. The film finishes where it began, echoing the theme of eternal recurrence, with more long shots of the undemolished Maldorais as it once stood, as well as a voice-over of Pvt. Benjamin's narration from the very beginning, and then the final credits roll.
