If I was to select one story to introduce new viewers to classic Doctor Who, I would choose Horror of Fang Rock. It is a story that is not only tense and holds the viewers' attention throughout the four episodes, it is not reliant on the special effects of the day, but is driven by pure dramatic tension.
Horror of Fang Rock is an exercise in perfect minimalism. There are only ten characters that appear throughout the entire story, including The Doctor and Leela, and never are all ten alive in the story at the same time (indeed, all but The Doctor and Leela die by the end of it, a first in Doctor Who history). There are a grand total of six sets - the lamp room, the crew room, a stairwell, Reuben's room, the boiler room, and the rocky area surrounding the lighthouse. That this tiny list of ingredients works as a gripping and claustrophobic story is a testament to the talents of writer Terrance Dicks.
Dicks is one of the series' more underrated writers. Put aside his speed written Target novelizations (and really, these should be praised for what they are, too. You try and write a novel a month based on someone else's scripts and see how well you do, and see if you can inspire a generation of future Doctor Who writers in the process). Dicks proved, with Malcolm Hulke's help, that he could make a fantastic story that spanned ten episodes and contained everything including the kitchen sink with 1969's The War Games. As superb as Patrick Troughton's finale is, Fang Rock is most likely the finest story that Dicks has ever written.
The lack of characters allows us to get to grips with each one of them, and when they each die, one by one, you feel their impact. Someone as noble, innocent, and likable as Vince would usually survive an average Doctor Who story, but is cruelly killed early in Episode Four. Adelaide, the least endearing character of the bunch, still has a horrible death scene that at least garners some sympathy from the viewer. Skinsale, though noble and heroic, is done in by his greed, but his death still leads the viewer too feel pity.
The atmosphere throughout the entire story is unabated in its tension. Dudley Simpson's sombre score accents the action where needed, but the soundtrack for this story is most often the sounds of the lighthouse foghorn and the unrelenting, crushing sound of the boiler. Even something as simple as the door to the boiler room is a portal of dread and doom. Many who leave through it don't come back, and those that come through bring death with them.
Paddy Russell directs her crew with unique precision. It might have helped that this story was recorded at BBC Birmingham, and the crew there were eager to go above and beyond to show their London counterparts that they were as good as, if not better, than any production crew in the UK. The performances from the cast are universally strong, and Tom Baker is at the absolute peak of his powers. He has never been better as The Doctor, before or since.
Horror of Fang Rock is not only a triumph for all involved, it is one of the finest examples of how so much can be made out of so little, it's one of Doctor Who's most criminally underrated stories, and one of the finest adventures in the long history of the series, old and new.