The Talons of Weng-Chiang

The Talons of Weng-Chiang is a reasonably popular Season Fourteen story arc. Written by Robert Holmes it features aspects of several different styles and story lines culminating together to make a brilliant fascinating adventure. The only adventure not to feature Tom Baker with his iconic scarf, The Doctor rather dresses akin to Sherlock Holmes, or at least the stereotype of Holmes. The story takes place in Victorian london, during a time when girls are mysteriously disappearing. It is implied that this could be the work of Jack the Ripper, though wether this is set during the time or shortly afterwards is never stated in fact. The Doctor and Leela intend to visit the theatre where Li H'sen Chang, the magician is performing. Chang being more akin to Fu Man Chu. Chang also has a living ventriloquist dummy, similar to the evil plastic monster doll in Pertwee's Terror of the Autons.
Eventually we find that Chang is working for a man claiming to be the god Weng-Chiang, a character who always wears a mask because of his disfigurement. Similar to the Phantom of the Opera. The Doctor (and Leela) work with a coroner called Professor Litefoot who is treated as a Watson style character. He is similar in appearance to the stereotypical Watson and at one point the Doctor even says 'Elementary, my dear Litefoot.'

Oh and there are Hammer House of Horror style Giant Rats in the sewers of London that eat people and are guarding the villain.

Normally I would say appropriating so much from else where would be a major draw back. It does not sound very original on the surface. Yet Robert Holmes manages to weave a truly original and interesting story that references all of these elements. There are heavy implications that the Doctor inspires the character of Holmes, for example. With all these elements what the audience really winds up watching is The Doctor (as Sherlock Holmes) versus Jack the Ripper (as the Phantom of the Opera) and Fu Man Chu.

What makes this story even better is the direction it goes in, the pacing it takes and the overall style of it all. It is a dark tale, portrayed in a gothic horror style with a perfect pacing for suspense and action, with a couple of great plot twists thrown in.
If you havn't seen the Talons of Weng-Chiang yet, I highly suggest that you do!