Boris Karloff delivers a damn fine performance in this gripping gem of British Horror. First off it should be stated that Karloff was a genius. He could provoke more fear from the audience with as little as a weird facial expression, than all of modern cinemas most expensive CGI technology. Secondly it should be stated that the less you know about this movie before watching it the better. The description here pretty much gives the whole thing away, so I'm glad I didn't read it before before watching this. Lastly it should be stated that this is simply a great mystery story, that will keep its audience guessing throughout. It did remind me of Dr. Jekyll and Mr. Hyde at times, but this had enough of its own thing going on, that it easily stands on its own, despite some minor similarities to other, better known horror stories. I'm surprised that so few people have seen this one, especially since it has been given the Criterion treatment. Either way I couldn't recommend this one enough to fans of the old school of horror.