Alright, here we go. We have the introduction of an important character to the Doctor Who mythos.
That’s right. Captain Yates of UNIT is here, a man who will, alongside the Brigadier and Sergeant Benton, um, do UNIT stuff.
No, I mean someone else.
That’s right! The Doctor has a new companion in the form of new lab assistant Jo Grant, who is the very opposite of Liz Shaw in every way. Liz was smart and professional. Jo is…kinda dumb and clumsy, and it’s a little odd that she even got a job with UNIT at all. The Doctor, initially, doesn’t want her, but the Brigadier isn’t wrong when points out that the Doctor doesn’t really need a scientist as an assistant so much as someone to hand him stuff and tell him he’s brilliant, and Jo can do just that. Plus, the Doctor doesn’t have the heart to fire her himself.
OK, no, there is someone else.
That would be the Master, another Time Lord with a TARDIS that actually has a working camouflage unit. He pops in, hypnotizes some people, sets some booby traps, and steals something important.
What is it? Um, a hunk of plastic that comes from the Nestene Consciousness, and could be used to make some more Autons. There’s some stuff involving radio telescopes, and the Master even shrinks one scientist down to fit into his own lunchbox. The Doctor was warned of the Master by another Time Lord, a jaunty-looking fellow in a bowler who just shows up without any sort of time machine, gives the Doctor some information, and leaves.
But then that clumsy Jo gets spotted by the Master, hypnotized, and told to take a booby trap back to UNIT. And she’s just opening it up when the episode ends…