
Ultraviolet takes place in the year 2078, in the years following a global pandemic of a blood-borne, highly infectious disease known as hemoglophagia. Those afflicted with the disease are referred to as “hemophages”, and have many super-human attributes similar to those of the vampires of legend. When the media began drawing comparisons, fear consumed the population. This led to the rise of the Arch-Ministry, a militant medical establishment which took control of the government and began rounding up and exterminating all infected citizens to contain the virus.
The heroine of the film is Violet Song jat Shariff (Milla Jovovich), a young woman who was infected with hemophagia, in the process losing both her husband and her unborn child. Violet is now an emotionally dead killing machine, hired by an underground resistance movement of hemophages waging a guerrilla war against the Arch-Ministry and its megalomaniacal, mysophobic leader, Vice-Cardinal Ferdinand Daxus (Nick Chinlund).
Infiltrating a government laboratory, Violet steals a weapon developed by the Arch-Ministry to exterminate all hemophages on the planet, only to discover the “weapon” is a child named “Six” (Cameron Bright), a young clone of Daxus (sixth out of a series of eight). Six is believed to be a carrier for cultured antigens developed to target hemophages, which Violet’s fellow hemophages want destroyed. At first Violet seems to regard the somewhat catatonic Six as merely a lab sample, but as Six begins to show increasing signs of personality a bond begins to form between the two. Her softer emotions begin to awaken once more as she grows fond of the boy, and he of her.
Violet breaks ranks with the hemophages and flees with the boy, believing that a cure for the disease can be reverse-engineered from the antigens. On the run from both the government and the hemophages, Violet’s only ally is Garth (William Fichtner), a hemophage scientist who is secretly in love with Violet. Garth, upon analyzing a sample of Six’s blood, tells Violet that the child has not been infected with anything that can kill or cure hemophages. However, whatever Six has been infected with, will kill the boy in a few hours.
Daxus recruits the other hemophages to retrieve the boy, revealing to them and Violet that the antigens in his blood are actually deadly to humans. With the hemophages nearly exterminated, the Arch-Ministry intends to engineer a new plague, to which they possess the only cure. This is being done to maintain their power, supposedly to prevent society from collapsing into anarchy if the Arch-Ministry becomes obsolete. Violet easily kills the hemophages, then demands the cure from Daxus. He refuses, instead offering to make her a duplicate of Six if she will give him the genuine article. Violet is not swayed.
Both Violet and Six are dying from their respective ailments, so rather than fight a futile battle against Daxus, Violet takes Six to a playground where the two spend the last few moments of Six’s life in an idyllic setting. Daxus and his men arrive just as Six dies. He shoots Violet and orders Six be taken to the Arch-Ministry’s headquarters, where he will be dissected and any helpful elements salvaged to aid in recreating the antigens.
Garth manages to revive Violet, but now that she is grief-stricken over Six’s death, she has no desire to resume her life as an unthinking killing machine. However, she is alerted by Garth to a newscast showing the day’s events, and when Violet sees the news footage of herself weeping over Six’s body, she recalls a tear dropping onto Six, realizing that he may not be truly “dead” after all. She mounts an assault against the Arch-Ministry’s headquarters to retrieve Six’s body. After loading her suit with enough weapons to wage a small war, Violet enters the Archministry and forces her way deep in the building, just as Daxus and his men are about to dissect Six.
In the lab where Six is kept, Violet has a final showdown with Daxus. Daxus attempts to use a flamethrower, which Violet defuses by extinguishing the pilot light with her own blood. He tips the odds in his favor by drawing a sword and blocking out the light from the windows. Daxus explains that he was one of the original lab technicians researching the hemophage virus, and after an accidental exposure, used the enhancements he gained from the disease to aid in his rise to power. Violet manages to level the playing field by igniting her sword with fuel from his flamethrower, sprayed on it when she first disabled the flamethrower, and spreading the flame to his blade. She finally emerges victorious when she sets Daxus on fire with his own discarded flamethrower and slices him in half.
In the end, Six is brought back to life by the hemophage virus, which was carried in her tears, the virus having immunized him from Daxus’ anti-human virus. Six reveals that he knows the cure for hemoglophagia, which can save Violet’s life. The two of them drive off into the sunset as the Arch-Ministry’s headquarters burn. Violet states that she is uncertain if she will die from her wounds or her terminal-stage hemoglophagia, but that evil-doers had better beware if she does not.