First Doctor Four story! And he's running, right off the bat, sometimes literally. I always liked Four. He's so cheerfully unconcerned with the possibility of total annihilation of himself, and swings between overly interested in events and concerned with the fate of humanity, to jolly and joking with monsters and their makers while still gathering information and getting things set up.
So there's this robot, see? It's been killing people and stealing things with no regard for human life, so they figure it must be inhuman-- and track down a robot-maker whose plans have been revived in the form of a 7-something foot tall silver bit of coolness that I want an action figure of so bad. Well, Sarah-Jane tracks it down and finds Ms Winters, the villain, who demonstrates that the Robot couldn't have killed anyone by ordering it to kill Sara-Jane. And that's the first cliffhanger.
Of course it doesn't; it's got the Azimov Laws that prevent it from harming people. But it gets fond of Sarah-Jane because she wants to understand it and treat it like a thinking creature, and as the plot develops and it realizes it has been killing people by taking out the 'threats to humanity' they've been sending it after, including the crazy scientist who did build it after all, it decides to kill all people-- except Sarah-Jane.
The Doctor, of course, has been leading UNIT around, trying to track it down and save Ms Smith, and mostly proves what and excellent new Doctor he is while SJS handles the nitty gritty of the plot-- but it's no less interesting for all that.
Over all, I really enjoyed Robot. Four is amazingly interesting to watch, even when he isn't doing much of anything, and I just love that the very first story he's in, he's the same wonderful lunatic as he was in the much later ones that I've seen. And Tom Baker never forgets that the Doctor is fond of both the Earth and it's people, and especially fond of Sarah-Jane. The story is compact, without much running around and getting captured again, which, as we know by now, is the mark of added-in scenes to extend the story. And it all makes sense. All the characters have reasons for being what they are.
And at the end, Sarah-Jane and Dr Harry Sullivan head off with the Doctor on off-world adventures, and the Brig looks sad in a 'I never get to go in the Tardis' way and says something about waiting around. Poor Brig.
This leads directly into the next story: Ark In Space.