It's a very picturesque opening -- lots of long lingering shots of an early-19th century coal-mining village, underscored by pastoral music as filtered through an '80s synthesizer. But soon we see some of the miners acting like jerks: the result of some sort of sinister process that's left a red mark on the miners' necks. It seems we're going to get Doctor Who's take on the Luddite riots.
Except not really, because it turns out that the Master is back. No explanation is given as to how he survived the events on Sarn -- allegedly writers Pip and Jane Baker included one, but Eric Saward cut it, in a fit of pique over the return of the Master yet again (can you tell he's starting to get frustrated with this job?). There's also no explanation as to why he's pretending to be a scarecrow out in the middle of nowhere...
Of course, the presence of the Master ends up distorting the entire story around him. We're no longer interested in what's going on in Killingworth; we want to know what the Master's up to. But this time, it seems he's not the only Time Lord around. We're also introduced to a renegade Time Lord called the Rani, who appears to be an amoral scientist, extracting a chemical from humanity for her own purposes -- the violent behavior is an "unfortunate side effect". The Rani, played with great superiority by Kate O'Mara, is clearly meant to be neither explicitly "good" nor "evil", but rather a scientist with no compassion or morality. It's a nice little twist on the sort of characters we normally get on the show.
However, if the Master was distorting things before, now that we've got the Rani involved, events truly get bent out of shape. The entire episode becomes little more than a backdrop to their arguments, and while the squabbling is certainly entertaining (particularly the Rani's comments on the Master: "You're unbalanced; no wonder the Doctor always outwits you", and "What's he up to now? It'll be something devious and overcomplicated. He'd get dizzy if he tried to walk in a straight line" being two highlights), it does unbalance things. And so it really doesn't help when the Doctor is also introduced and all three start sniping at each other.
And of course, this is our first Pip and Jane Baker script, which means there are lots of examples of florid dialogue to join in with at home (the favorite probably being "Fortuitous would be a more apposite epithet!"). Pip and Jane clearly love language, but it does make a lot of the dialogue very unnatural-sounding (and that's before it gets put through a broad Geordie accent for all the locals). But, contrasting this, their characterization is very good, and the Doctor is probably the most like the traditional Doctor -- which is to say, not deliberately alien -- he's been this incarnation (although the joke about a "hyperactive Peri" does seem a particularly sixth Doctorish thing to say). This does make this story a lot more fun to watch, and it helps set him apart from the Rani and the Master. (That said -- and it's definitely not Pip & Jane's fault -- who thought it would be a good idea to make the sixth Doctor's signature verbal trait to repeat a word three times at increasing volumes?)
There are some good moments here and there (the stuff with Lord Ravensworth is quite nice -- and you can see, as the Doctor takes off his coat and puts on a dirty one (around the 30 minute mark), the cats that have been added to the coat's lining for each completed sixth Doctor story), and the arguing is rather entertaining, but so far, the interaction of the three Time Lords swamps everything else in this story.