Kindly Dr. John Garth (Boris Karloff) is found guilty of a mercy killing and sentenced to hang. While in prison he experiments in trying to find a serum that halts old age. He uses the blood of an executed murderer and tries it on himself. He is then pardoned and finds the serum works...but it turns him into a cold-blooded killer which he has no control over.<br /><br />This is pretty much a forgotten movie and it's easy to see why. It's pretty slow and dull with terrible dialogue and questionable science. Also it's (technically) not a horror movie--it plays more like a melodrama with horrific touches. Wonderful actress Evelyn Keyes is in here too but is given nothing to do. Karloff single-handedly saves this from total disaster. He's just great in his role--he makes the worst dialogue sound like Shakespeare! Also when the killing urge takes over you can actually see the changes in his face and mannerisms and there are also some nice atmospheric scenes at the end. There's a funny lapse in continuity--Keyes finds out by the morning paper about a murderer--but a scene outside the house shows it's night time! This is really only for Karloff fans. I give it a 4.