THE INVISIBLE KNIFE is definitely one of the better of the Colonel March episodes and a big step up from the stupid kidnapped poodle story that preceded it. This one's an involved little thriller in which murder is at the fore and there are plenty of plot ingredients to fill up the 25-minute running time. It also so happens to be directed by Hammer stalwart Terence Fisher who gives it a classy look.
March finds himself involved in the case of a man who is associated with many deaths occurring around the globe. One of them involved the titular weapon and another a dead parrot, amusingly enough. March traces the case to a pet shop owner, and it all bubbles along quite happily to an unusual and exciting climax involving devil worship and a big twist. Once again this is a story that flirts with the supernatural without ever being explicitly so and Karloff has more to get his teeth into than usual.