A team of scientists (George Hamilton, Suzanne Pleshette, Richard Carlson, Earl Holliman, Nehemiah Persoff, and Arthur O'Connell) are working on a top-secret project testing astronaut endurance. They are visited one day by their government liaison Arthur Norlund (Michael Rennie) who is skeptical of the worth of the whole project, other than the ideas of the team crack-pot, anthropologist Henry Hallson (O'Connell) who is convinced by his survey studies that one of the subjects has paranormal abilities. His outbursts embarrass the entire board, especially Dr. Tanner (Hamilton) who tries to beat down the doctor's ideas at every opportunity. However, a simple test proves that one of the scientific team has extraordinary mental powers.
Before you can say "Agatha Christie's 'Ten Little Indians'" the scientists start being knocked off in strange ways that only we, the audience, are privy to. First Dr. Hallson is found dead, centrifugally squished in a centrifuge run amok. Then Dr. Tanner is fired from the project, accused of never having attended college, and faking his way into his position. He teams up with fellow researcher (and main squeeze) Marge Lansing (Pleshette) to try and track down who the murderer could be. In the meantime, more of the research team end up incapacitated, and it becomes readily apparent to Tanner and Lansing that they're going to end up on a slab unless they can find the killer. But who is it?
The movie is quite clever in how it clicks along, even if the love story feels a bit tepid, and Haskin's stage sense is always assured at making the strange either commonplace or particularly fascinating.* For instance, the scientists work in a facility where their offices are separated by glass, so everybody can keep tabs on everybody else, making hiding the killer a difficult project. Once Tanner is fired, however, the confining space is taken out of the equation, and the individual attempts at messing with people's minds are given free reign and can come out of anywhere...and nowhere at the same time.
As far as the acting is concerned, it's a bit cheesy, with O'Connell over-emoting until you wonder about his credentials, and Hamilton smolders throughout, as if told he'd be the leading man, but not told how. He's at his best convincing us that the illusions he sees are real, and the horror/confusion that he feels play across his face. That's when he truly bonds with his audience, and is the filmmakers' best asset in making the movie come across.
* Haskin had worked with Disney live action films, and did the more superior episodes of the original version of "The Outer Limits" as well as the first pilot for a little series called "Star Trek."