A strange, metallic cylinder is stored at a laboratory, waiting to be tested. It belongs to the aliens, and they are willing to kill in order to get it back.



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Episode cast overview:
Harry Swain
Colonel Frank Griffith
Milton Selzer ...
A.J. Richards
Diane Oberly
Walt Anson
Douglas Henderson ...
Lieutenant Farley
Leo Rinaldi
Air Crash Investigator
Michael Harris ...
Mail Truck Driver
Raymond Guth ...
Guard #2
Mel Ruick ...
Minister (as Melville Ruick)
Ron Doyle ...

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A private plane crashes, but the investigators can't find a record of the flight, nor can they find a body - even though it was a crash no one could have walked away from. What they do find is a cylinder made of some strange metal they can't identify. They have it sent to Sperrick Laboratories. It arrives, but not without incident. Someone tried to hijack the mail truck, and two security guards were killed. David Vincent arrives at Sperrick to investigate. He is certain that the aliens were behind the attempted hijacking and that what they wanted was that strange cylinder. He is also certain that they will try again. Vincent finds allies in a security guard and a woman scientist. But as always, he never knows which of his friends are real and which are enemies in disguise. Written by J. Spurlin

Plot Summary | Add Synopsis


Drama | Sci-Fi | Thriller




Release Date:

7 March 1967 (USA)  »

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Technical Specs


Sound Mix:


Aspect Ratio:

1.33 : 1
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Did You Know?


William Talman's final TV role. See more »


Just before the Lincoln sedan arrives at the airport, the view through the windshield shows the rear view mirror has been removed: only the circular pad is visible. When the car is next shown at the airport, the outside view looking in, shows the mirror in place. See more »


Narrator: [Opening Narration] A small, private plane crashes, leaving no trace of its victims. A mail truck is attacked - two security guards killed. A killer disappears in a burst of flame. News items too incredible to be taken seriously - except by one man. David Vincent's only possible conclusion: the killers had been aliens and, for reasons of their own, might even be attending their victim's funeral.
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User Reviews

Another Gripping Chapter of The Invaders
13 September 2015 | by (Out There in the Dark) – See all my reviews

The 8th chapter of Season One, "Quantity: Unknown" has some original plot touches and uses a number of eye-catching locations, including a great psychedelic night club and a monumental structure featuring a high waterfall.

The cast includes James Whitmore, Susan Strasberg, Barney Philips, Milton Seltzer and William Talman in his last filmed appearance. All are excellent. And as always, Roy Thinnes is a standout.

This episode might recall the great film noir KISS ME DEADLY, as sinister forces go in search of a mysterious metal cylinder. It's easy to imagine TV audiences of 1967 being gripped by this one. It really never lets up and it has a stronger emotional component than some previous chapters.

A visually arresting and exciting episode.

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