The introduction to this episode was fantastic--starry and thrilling to watch. I also loved the teleportation--very effective despite a very small budget. The only problem is that it let you know then and there that Mr. Xeno was a BAD man---a very, very bad man indeed! In hindsight, I think it might have worked better had this only been revealed later in the show--to give it suspense. Still, it's one of the best episodes of the series.
Mr. Xeno then arrives at the home of a couple (MacDonald Carey and Marion Ross) and introduced himself as a special tutor sent by the government to work with their genius son. They agree but after some time, the father is a bit concerned--weird sounds are emanating from his kid's room and Mr. Xeno just seems to 'pop in' with no notice. Later, however, the father realizes Xeno is not human. The problem is, no one believes him, his son has now been pitted against him and there is some evil brewing. What's next? See this one for yourself.
All in all, there isn't much to dislike about this one. Fine acting, exceptional writing and a story that keeps you on edge--this is one to see.
UPDATE: I just saw an old episode of "Tales of Tomorrow" (available through the public domain at archive.org) that was VERY much like "The Special One"! In fact, it would appear to have inspired this "Outer Limits" episode. Try watching "Many Happy Returns"--you'll see what I mean that it seems to have inspired this show a decade later.