Doctor Who: The Seeds of Death (1969) directed by Michael Ferguson and written by Brian Hayles
Second Doctor Patrick Troughton lands on Earth in the late 21st century with companions Jamie (the Scottish highlander) and Zoe (scientific wiz). They discover the planet has become completely dependent on T-Mat, a sort of teleporting system that has reduced every other form of transportation to museum pieces. The system starts having problems because the relay station on the moon has been overrun by invaders--the Ice Warriors of Mars! Taking over the moon base is only the first step in their nefarious plan to conquer the Earth.
The six-episode series is a mixed bag. The Ice Warriors' costumes look a bit fake (baggy rubber suits that make their movement awkward) but their hissing, whispery voices (they are a reptilian race) are effective. The plot moves at a good pace and has only one or two head-scratchingly bewildering moments. Patrick Troughton is a fun Doctor, able to do comedy and drama without looking silly. Bigger issues like the overextension of technology and the need for adaptability are nice themes which naturally flow from the story.
A fun if not outstanding series.