So, let’s get the obvious out of the way first. This serial is set in late 19th century London, and there’s a character who is supposed to be Chinese obviously being played by someone who is not the slightest bit Asian.
This could get ugly.
That man is a stage magician named Li H’sen Chang. He dresses like a stereotypical Chinese man and speaks like one too. Yeah, this will get ugly. Looks like he does some ventriloquism too.
But he may also be evil since a cabbie burst into the theater he works in, demanding to know what happened to his wife. The cabbie’s wife. Not Li H’sen Chang. That man is sent away, but there are strange things going on around this theater. There are reports of large things in the basement, and the owner swears he saw the ventriloquist dummy move and even bleed.
Also, the dummy on its own attacked the cabbie.
Confused? Maybe you should be! Time for the TARDIS to show up. The Doctor wants to introduce Leela to some of her ancient ancestors. He even made her change her clothes to fit in, something she and who knows how many young male viewers of this show don’t care for. The Doctor himself is going for a Sherlock Holmes look. Maybe they’ll investigate a crime. The Doctor does want to take in a stage show.
And then, en route, they find a dozen or so Chinese men taking a body away. The Doctor tries to stop them and gets smacked around a bit. Leela jumps in and does better. She manages to restrain one for when the constable arrives and arrests all of them. And since this is the Doctor, he sees no harm in telling the man the complete truth. He even offers to translate for the Chinese man.
That won’t be necessary as Li H’Sen Chang shows up. The Doctor thinks he’s seen him before, but Chang makes some comment about how Englishmen think the Chinese all look alike. That just makes the Doctor a little confused, but he does eventually get the name right.
Of course, he says he last saw the guy 400 years ago…
Maybe if he paid more attention, he would have seen Chang slip the prisoner some poison. Of course, the Doctor then gets on the police’s good side by sniffing the exact poison out and finding a gang tattoo on the dead man.
By then, the cabbie’s body came in, and it looks like something large tried to eat him. The Doctor heads out, telling Leela to stay behind. She doesn’t listen but does stop an assassin, so the Doctor changes his mind. Then the Doctor remembers a bit more about Li H’sen Chang. He might have been a god or something. Known for abundance.
By then, the two have opened up a manhole and climbed into the sewers. And heck, they find the thing that chewed on the dead cabbie: one very large rat.
I think it’s a regular size rat in a model, but it actually looks pretty good, so I’m fine with whatever the show did.