A barely conscious, unidentified man is brought into intensive care, where a doctor and a nurse tend to severe burns on his hands and decide to administer oxygen. The scene quickly shifts to a delirious street episode, where the man encounters an old classmate named Jiří Tomeš. The man, who is revealed to be Karel Höger as Prokop, speaks incoherently about a blast and something he calls krakatit.
In a dreamlike sequence, a university professor questions Prokop about krakatit. He explains that it is a powerful explosive named after Krakatoa and even recites a rough formula, a detail that Jiří secretly notes down. When Prokop wakes, he finds his door answered by a veiled woman who asks him to carry a letter to Jiří. We soon follow Prokop as he travels to visit Jiří’s countryside doctor father, aided briefly by an old mail carrier who helps him through the snow. Prokop’s strength falters, and he collapses, leaving him to be cared for by the doctor and his daughter, Anči. During his slow recovery, Prokop cannot recall what happened, and the memory remains shrouded until he reads a newspaper story about krakatit being marketed by a mysterious figure named Carson.
Eduard Linkers as Carson explains that Jiří had sold Prokop’s krakatit stock and the accompanying formula to Balttin Works, a distant weapons company. Their experiments reveal that krakatit can be detonated remotely via high-frequency signals, but they lack the practical production method. They press Prokop to work with them, offering employment to continue the research. When Prokop refuses, Balttin forces him to the royal Balttin palace to work in a chemical laboratory.
At the palace, Prokop enters a burgeoning romance with a princess, commonly referred to as Wilhelmina Hagen, a relationship that becomes entwined with his obsession. Yet his heart also yearns for the veiled woman he met earlier, whom he cannot forget. The Balttin executives propose a dangerous bargain: Prokop would be granted a marriage arrangement with the princess if he surrenders krakatit. Enraged, Prokop destroys the laboratory where he has been held, and with his coat loaded with explosives, he confronts the princess—whose face dissolves in the chaos. He manages to escape the palace with assistance from an ambassador, Jiří Plachý, who portrays the d’Hémon figure.
On the run, they encounter a secret circle of former world leaders and profiteers who worship war and hail Prokop as “Comrade Krakatit.” As the crowd scrambles for the krakatit powder, Prokop and d’Hémon slip away and briefly cross paths with the veiled woman once more. They ascend to the top of a hill made of magnetite, where Prokop’s old laboratory has been relocated to a hidden radio station. There, d’Hémon persuades Prokop to press a button, unleashing stockpiles of krakatit to explode across European capitals. The explosions are so powerful that they seem to foreshadow a controllable war, a plan that shatters Prokop’s trust as d’Hémon vanishes.
Alone, Prokop finds himself in a bleak, concrete landscape and eventually reaches an enclosed factory. He asks to see Jiří Tomeš and is refused, but he does meet a lab assistant, to whom he hands the letter from the veiled woman. He then walks away as the factory explodes in the distance. An old mail carrier appears again, offering a lift and urging Prokop to invent something that makes people’s lives easier instead of killing them. Back at the hospital, the doctor reports that Prokop’s breathing has returned to normal and that the oxygen mask can be removed, signaling a rare moment of peace after a harrowing chain of choices.
