The one episode that ran near the end of the series and that I remember vividly, though I forgot the title concerned a group of scientist in a remote jungle location. They are hounded by an invisible creature that sucks blood. They are able to capture one and make a plaster mold of it. They learned that an ordinary pesticide will kill the creature and are now able to leave their compound. As they do so the camera pans to the plaster mold of the creature and I didn't sleep that night!! It was a giant bug with huge fangs!!
Review of Tales of Tomorrow
