Recap: If you’ve missed earlier posts and are baffled by the numbering, in a break with the accepted style of talking about The Avengers, I consider the program’s sixth season to be those fifteen episodes shown in America from January through May 1968. I bet at least three people get aggravated about this.
Further recap: John Bryce had briefly taken over production duties for the program, and asked adventure teevee veteran Terry Nation to contribute. “Invasion of the Earthmen” was the second of three that Bryce worked on. It was made while Linda Thorson’s hair had been bleached blonde for the role. Since cooler heads decided that her natural color would be just fine, this required Thorson to wear a brown wig, pretending that’s her real hair, in some new scenes added in which she decides to wear a blonde wig, which is actually her real hair, for this mission.
Brian Clemens had more than just a curiosity about the hair to deal with. This story is a complete turkey. It looks just fine, and our heroes engage in a couple of impressive fights, but there’s barely a plot to this adventure, and what plot we get is not necessarily a villainous one. Steed and Miss King are investigating Alpha Academy because one of their colleagues, a Mr. Grant, has gone missing while investigating the school. But we’re never told why he was looking into them. There’s a weird sense that we’re supposed to be alarmed or appalled that the villain is training young astronaut soldiers, but… is that a problem? Is that illegal? Mr. Grant gets killed by a hilariously fake boa constrictor, and they cover it up, but they never tell us why they’ve covered it up.
I guess we’re meant to be worried by the menace of the little fascists-in-training, and impressed by Nation’s reuse of some go-to plot elements from his sixties episodes of Doctor Who and The Saint, but there’s no meat in this story at all. Our son liked the fights and the creepy tunnel, and thought it was pretty exciting. As long as you don’t look closely, sure.
Fire Breathing Dimetrodon Time 
There’s a character named Trump in this episode, although unless someone pointed that out to you, you would never know cause he barely speaks. Think about that in the context of the episode and specifically when the leader is speaking to the woman, telling her all his plans.