In Victorian England, a philanthropic scientist, Sir Hugo Cunningham, Robert Stephens, sits at the heart of a parapsychological society that tests psychic phenomena. Their latest project involves photographing people at the moment of death, and the resulting images reveal a strange smudge hovering around the body. While the group regards this as evidence of the soul leaving the body, Cunningham remains skeptical, craving a cold, scientific explanation for what they’re seeing.
At a riverside party celebrating his son’s engagement, Cunningham films with a camera of his own invention. The celebration turns tragic when his son and the son’s fiancée die in a boating accident. When Cunningham reviews the footage, he notices that the blur not only accompanies his son but moves toward him as if drawn in rather than released. He concludes that the blur is not a soul but a looming force he terms an asphyx — a personal Grim Reaper reputed in Greek mythology, which arrives for each person at the moment of death. This radical interpretation sets him on a perilous quest to trap and control mortality itself.
While filming a public execution, Cunningham activates a spotlight of his own design — phosphorus stones fed beneath a drip irrigation valve. Watching the film again with Giles Cunningham, the adopted son of Sir Hugo, and Christina, his adoptive sister, they observe that the condemned man’s asphyx was briefly held in the beam. Cunningham theorizes that a specific energy released by the combination of phosphorus and water can suspend an asphyx. If correct, this discovery could allow a person to become immortal so long as their asphyx remains imprisoned.
Cunningham and Giles manage to capture the asphyx of a dying guinea pig and seal it within the family tomb. Seeing a path to true immortality, Cunningham tasks Giles with helping him capture his own asphyx. He orders the construction of an impenetrable vault door on the family tomb and instructs Giles to seal the asphyx inside so no one can ever release it. To summon his own asphyx, Cunningham subjects himself to a deadly experiment using an electric chair. Yet Giles has only experience in trapping asphyxes with two people, and he relies on Christina, his adoptive sister, to help with the experiments. Christina is horrified by the procedures but agrees to participate when Cunningham offers to bless a marriage between her and Giles if they allow him to make them immortal.
The plan hinges on the notion that imminent death can summon an asphyx. To trigger the effect, Christina is placed under a guillotine operated by Giles. Disaster strikes when the guinea pig gnaws through a hose feeding water to the phosphorus stones, causing a malfunction. Christina is decapitated in the ensuing chaos. Grief-stricken, Cunningham begs Giles to open the vault and free the asphyx, but Giles has his own terms: immortality first. In truth, he no longer wishes to live without Christina and sabotages the equipment. As Cunningham attempts to gas Giles to force the summoning of the asphyx, he discovers the apparatus won’t work. He switches off the gas and introduces oxygen instead, hoping to save Giles. A match lights an explosion that destroys the machinery and kills Giles, ending the immediate danger but leaving behind a ruined dream.
Cunningham then destroys the vault’s access code, deciding that immortality has already become God’s punishment for the deaths of Giles and Christina. In a stark framing sequence set in the 1970s, a deformed and aging Cunningham roams the streets of London with the guinea pig. He walks into the path of a car collision that kills both drivers, yet a responding police officer is astonished to find Cunningham, crushed beneath the wreckage, still alive.
This tale intertwines obsession, science, and the peril of playing with mortality, tracing a descent from measured inquiry to a catastrophic moral reckoning as the relentless pursuit of immortality backfires in the most irreversible way.
