This is an intersting Third Doctor tale starring Jon Pertwee first broadcast between 13 March and April 3 1971.
Beware of Greeks bearing Gifts is the old saying, but in this case it is the Autons, with a material called Axonite which brings with it the promise of solving all the earth's problems of food shortages.
Before you know it of course, there is more to it than that and soon the Axon plot is uncovered. The Master too, has a role to play as the two-faced, double-crossing, Timelord wriggles from his situation as a captive of the Axons and ultimately makes good his escape.
The Axons, similar to the Autons as part of a single entity are looking for an energy source and earth just fits the bill. The story highlights the fact that appearances can be deceptive as the Axons adopt a beautiful gold form which transfixes their human hosts and undermines their natural hostility and suspicion. The other human trait of greed, particularly when confronted with getting something for nothing, is also highlighted by this story as well as the ruthlessness which humans adopt when trying to get what they want.
However, the adage of all that being glitters is not gold holds up when eventually the humans find that they have been sold a pup. Almost too late, they fight to defeat the Axons who have reverted to their natural form with more than a little bit of help from the Doctor.
The moral of the story clearly is that we can get by without a little bit of help from our friends (or otherwise).
My only complaint about this story is the way in which this, and other third doctor stories, is another one of those 'the biggest threat to the human race than the world has ever seen'. Other than that it is a preety good well worth watching adventure.