Several scientists around the world, including Britain's Professor Geoffrey Munro (Warren Mitchell), have died of mysterious, explosive, brain haemorrhages - just as they were about to make major breakthroughs.
All were working on trying to crack the scientific formula that would allow individuals to "project themselves through thought" to alien worlds... what we might call today "astral projection".
Following Munro's sudden demise, newly-married theoretical physicist, Dr Mark Davidson (John Neville, probably best known for his portrayal of Hieronymus Karl Frederick, Baron von Munchausen in Terry Gilliam's 1988 The Adventures of Baron Munchausen) is promoted to take his place in the project.
However, state security - in the form of the secret service's wonderfully mannered Major Clarke (Patrick Newell, who would go on to play 'Mother' in The Avengers, from 1965 to 1969) - is suspicious of Davidson's whirlwind holiday romance and his new Swiss bride, Julie (Gabriella Licudi), about whom no records can be found.
There's also the fact that Julie sleeps with her eyes open, never blinks, has no pulse, cries acidic tears, is immune to extremes of heat, and scares children.
The clues are there that there's "something" about Julie, but love-struck Mark refuses to accept it, despite proclamations from both Major Clarke and Mark's colleague, Prof. John Lancaster (Philip Stone).
Nevertheless, regardless of his blind spot in regards to his new bride, Mark does reach the conclusion that if scientists on Earth are trying to reach other planets psychically, perhaps alien races have already come to Earth using the same method.
And perhaps they want to stop Earthlings gaining this ability to travel the cosmos.
But it's not Julie, right?
A tight, low-budget, black-and-white sci-fi thriller, 1963's Unearthly Stranger shares themes and ideas with both Invasion of The Body Snatchers and HP Lovecraft's story The Shadow Out Of Time.
Events kick off in media res, as a sweaty Mark races back to his office to document all he has learned via a reel-to-reel recorder.
This then allows the film to flashback to the main story - which, itself, contains a secondary flashback to Mark's first encounter with Julie (which bears many of the hallmarks of a classic UFO encounter).
The whole shindig is so compact that it feels like a 76-minute Twilight Zone episode rather than a movie, unburdened by spurious sub-plots and the need to slowly establish character and motivation.
This brevity is something often lacking in modern filmmaking.
This brevity is something often lacking in modern filmmaking.