Such was the producer's faith that the upcoming twelve-part The Daleks' Master Plan was going to be the biggest story is that they've given us a Doctor/TARDIS/companion-less story that serves as a prologue to that episode. It's referred to as a one-parter, but really if The Myth Makers wasn't sandwiched between them it would be treated simply as the first episode of The Daleks' Master Plan, which is basically what it is.
After the lighthearted Season 2, and the comedic turn by the Daleks in The Chase, this is a shock to the system. It's a story where the hero shoots two of his own men dead and is then killed himself, leaving viewers wondering whether or not everything he achieved in the story was for nothing. In place of the Doctor, the main character here is Space Security Agent Marc Cory, played by Edward de Souza. Cory has landed on the planet Kembel and is investigating a possible Dalek presence. He and the other agents battle against the poisonous Varga plants, which will consume them if they get stung. The Daleks, meanwhile, meet with representatives of the Seven Planets and discuss the death of the human agents and the conquest of Earth.
This is Terry Nation's bleakest episode yet. When it becomes clear that the TARDIS is not going to appear, viewers have to accept that the Doctor isn't going to arrive and save everyone. And that's the most horrifying prospect of all. De Souza is good as a temporary lead but we don't get to know Cory beyond his willingness to kill for the greater good and his determination to save others even if he knows he is going to die.
I don't rate this story highly, I'm afraid. I almost don't want to rate it, because it doesn't feel like a full story, and it isn't. Plus the Doctor isn't around which is just wrong.
Special praise for the sound designer - the jungle on Kembel really came to life on audio. Fantastic.
Horror quotient - Without the happy ending, this is very dark story. The Varga plants sting two agents, and the story shows the horrific effects which ensue. Then they die. Doctor Who hasn't been like this before, and it's unsettling.
Comedy quotient - Would have been out of place.
Drama quotient - The situation builds up and doesn't really have a resolution. This is a very tense story and seems to be building up to something big - and it is.
Great as a prologue, relentlessly grim and ultimately unsatisfying as an individual story.