Police are called to a car accident, and discover in the wreckage that a man is trapped between the two vehicles; when they pull him out, they're amazed that he is still alive. About a hundred years before, in Victorian times, Sir Hugo (Robert Stephens) is bringing his new fiancée back to meet his grown children, Clive (Ralph Arliss), Christina (Jane Lapotaire) and the adopted Giles (Robert Powell). Sir Hugo is a scientist experimenting with photography, and he has invented a device that takes moving pictures. But something is bothering him about three slides he has, all of which show people at the point of death with a mysterious shadow over each of their bodies. What could this phenomenon be? And can he capture it on moving pictures?
Who wants to live forever? Be careful what you wish for, especially if you suffer regrets, is the message of The Asphyx, a musty horror written by Brian Comport. Setting out the familiar tale of things man was not meant to know, the action sees Sir Hugo (a wildly overacting Stephens) discover that the enigmatic smudge on those photographs is in fact the spirit of death, what the Ancient Greeks called the Asphyx. With his booster contraption he can capture the apparition and keep it locked up, so that the person it was coming for will live indefinitely, or until the Asphyx is released.
Just in case you're in any doubt about the film's title, the characters repeat it around a hundred times throughout, but the first time we get to see the critter is when Sir Hugo replays footage of a tragic boating accident that has claimed his wife-to-be and his son Clive. He was filming them messing about on the river, you see, and looking at the footage (while grief-stricken, naturally) he notices the smudge swooping down on Clive as he died (thanks to a hitherto unknown zoom lens on his primitive camera). This gets Sir Hugo thinking, but then one of his friends arrives with news of a hanging to be held the next day.
Sir Hugo goes along to provide footage of the execution, and to fuel the reform movement's belief that this is a barbarous act, but, what do you know? He captures an Asphyx with his booster just as the trapdoor opens, delaying the criminal's demise. Next up, he experiments on a guinea pig, and successfully captures the rodent's Asphyx. The gloomy circumstances of Victorian life are illustrated with references to the orphanage where Giles grew up, the capital punishment, and tuberculosis, which is what Sir Hugo's human guinea pig is suffering from. That experiment fails when the man resists, so Sir Hugo has no choice but to trap his own Asphyx (which certainly brings tears to his eyes).
While it's never boring, the film mainly keeps your attention through its mixture of the morbid and the ridiculous. When Giles assists Sir Hugo in trapping his Asphyx, how were they going to do it without the help of a third party (the innocent Christina barges in at the critical moment to save the day)? That's nothing compared to the unintentional hilarity of the guinea pig's revenge, striking a blow for anti-vivisectionists everywhere, after Sir Hugo has persuaded the now-in-love Giles and Christina to go through with the process themselves. And what were those two cars doing driving straight at him, anyway? It's not a bad set up, and the Victorian paraphernalia is nicely realised, but this is a silly film all over. Music by Bill McGuffie.