Some time in June 1964, mercenary Irish-born British Major Thomas Harry, better known as Major Mad Harry, is rehired by the Congolese in-waiting Prime Minister, MoÃ¯se Kapenda TshombÃ©, a wealthy man, whom he meets in his Pink Palace in the Katanga Province for the second time in three years, supposedly to salvage the fate of the foreign hostages, including a few Americans, in the three-storey HÃ´tel du Lac, in Albertville â a town on the western shore of Lake Tanganyika â already attacked and seized by the ruthless rebels who call themselves the Simbas, and who are led by Gaston Soumialot and his General Nicolas Olenga. But in reality Harrys pressing mission is to retrieve the secret Belgian gold cache, all in bars packed in ten crates, worth fifty million dollars, from a banks vault only known to four protagonists: TshombÃ©, the CIA station chief, the Union MiniÃ¨re director and Harry himself. Incidentally, a Belgian named Antoine van Bilsen, who happens to be the bank Director, is forced to look after the cache that is now in the hands of the rebels who hold his wife, Beatrice, as a hostage in Alberville.
Harrys subordinates, notoriously named Les Affreux, the Terrible Ones, include an Afro-American man named Captain Cyrille Cernuda, of ArmÃ©e Nationale Congolaise, who turns a true friend, and a drunkard Irish-born Doctor, Joseph Barnes, who has hardly given up drinking since his wifes car crash back in Dublin years before his arrival in the Congo. Reluctantly, he also takes along two other men, one is the snoopy Lloyd Garrison who works as a correspondent and photojournalist for Scripps-Howard, then Americas largest chain of newspapers, whose flagship was The New York Herald Tribune, and a Ku Klux Klan leader and old-time foe of Harrys bygone days, an American-born Major called Lawrence Mike Williams, on a mission because he needs both men: Garrison because of his knowledge of the town and the hotels whereabouts, and Williams because of his band of mercenaries and his military expertise and leadership skills.
TshombÃ© also gives Harry and his hirlings the use of a matte black wood-burning train, equipped with sufficient firepower, along with government soldiers on board, and leaves the only train station in the southeastern city of Ãlisabethville for their doomed destination, Albertville. On the way, the train is attacked by a United Nations peacekeeping Alouette chopper piloted by two Swedish men that forms part of the UN air force. Harry then picks up a beautiful blond Belgian missionary damsel named Maye Michels in his Belgian-made tricycle TricycleSpankenTruppen after the mercenaries train finds her running wildly along the railway line in the midst of hills and bushes, escaping from her chasers, a Simba patrol driving in a Soviet-made jeep, part of the rebel bands that earlier attacks her small village church and burns it down and kills the rest of the missionaries. Meanwhile, Major Williams, who resents Harrys leadership, begins to cause trouble because the American sneaks into one of the jeeps loaded with the gold cache.
Things come to a boiling point when the American makes a romantic advance, which Harry interrupts. Harry and Williams then fight an inconclusive duel which involves a chainsaw. First, Williams attempts to use it on Harry who then desperately takes his turn to use the chainsaw. Harry is prepared to kill Williams but stopped by his close friend, Cernuda. But there are further complications when the mercenaries reach the town. Firstly, the gold cache in a time-locked vault delaying the departure of the train, and secondly, Garrison and Cernuda attempting to have the hostages in the hotel freed.
Before travelling into the bush, Harry and Michels along with three of his men stop by the rear side of the bank and secretly carry off the cache, leaving behind Garrison and Cernuda who drive in another jeep and stop by the hotel. Using a Simba disguise, Cernuda takes in Garrison who now pretends to be his prisoner. But as Cernuda leaves, Garrison refuses to abandon the hostages in the hotel, with its rooms full of sickening scenes of rape, murder, drunkenness and torture, and agrees to stay behind to help them to escape through a safe passage. Just as Garrison leads the hostages stealthily to a safe haven in the midst of low-ling hills around the town, he is told by one of the Belgian hostages that her son is left behind.
Garrison prepares to take the risk and treks back to the hotel to save the little boy in the hotel. But as he attempts to save the last hostage, the Simbas manage to capture Garrison and show no mercy and have him tied up to two trees in the town centre. With Garrison at the mercy of the Simbas, Harry reluctantly agrees to let one of his marksmen on the train to shoot Garrison to stop him from further torture in the hands of the Simbas who are now cutting him alive with machetes. Back in the town precious minutes tick by as the train hurriedly picks up the hostages.
The delays in the bank and the hotel eventually allow the other Simba force, loaded in Soviet-made jeeps and trucks travelling on a dirt track, to catch up and begin attacking the train and Harrys men. Finally the heavily-laden train, which is loaded with the gold cache concealed in a jeep and the residents, slowly leaves the station under small arms fire. But just as it is nearly out of range, a mortar round destroys the coupling between the last two carriages. Agonisingly, as the rest of the train picks up speed and steams away, the last coach with most of the hostages on board slowly comes to a stop before rolling downhill back into the Simba-held town.
Before the train leaves off, Harry loses Bilsen and his wife and some of his men to the waves of the wild Simbas who now attack the train on foot from the rear. And as the Simba army leads a raid to retrieve the gold from Harry and his men, the train eventually leaves. Following a rail line diversion involving two purloined trucks by the Simbas, the train stops halfway in the middle of nowhere and by the time Cernudas men attempt to have the rail cleared off, the second wave of the Simbas suddenly launches attacks in three fronts. Harry and his men are too few to face the wrath of the spear-waving Simbas who manage to kill many, including Doctor Barnes.
In the end, the train leaves to safety. When the train runs low on fuel, Harry and one of his men, Sergeant Rolf Steiner, once a member of the Hitler Youth, leave in a jeep to get hold of army trucks from a nearby Congolese military camp to carry off the rest of the hostages and a few men he is left with. Little does Harry himself know about the gold cache loaded in his jeep by Cernuda who always mistrusts Williams. In his absence, Williams kills Cernuda with his long knife and now takes on Michels, slapping her in the face several times, in the mistaken belief that both know about the whereabouts of the gold cache. Empty handed, Williams drives into the bush in one of the jeeps. When Harry returns to find his friend dead, he is filled with murderous revenge. He pursues Williams in his favourite tricycle and after a vicious brawl Harry kills him with the same knife with which Williams strikes Cernuda. Harry then returns to the truck convoy. With his job done, Harry reflects on himself, feeling the guilt of vengeance, and turns himself in for a court-martial for his action.