Monferno is a 4 hour long serial about a group of people politely asking a mad scientist to stop trying to destroy the planet by drilling into its core. A four-at-most-parter stretched and padded out to being a seven-parter, but still GOAT.
Plot, as it wereEdit
During one of the Doctor's attempts to repair his TARDIS, he travels into another dimension, a Britain in which the country is controlled by a strict totalitarian regime, ruled by Brig Boss and an evil version of the doctor, if you accept the novels as canon. In all seriousness the story is amazing despite dragging it's ass at times by repeating various scenes, such as..
"PROFESSOR STAHLMAN PLEASE STOP DRILLING"
"Where do you come from?"
"I don't believe you"
It is arguably one of the darkest stories of Doctor who since a human race dies a horrible firery death, and we see these characters at their most desperate and pitiful. It handles the appocalypse a lot better than other stories I could mention *cough cough* Last of the Time Lords *cough cough*. Although it does end on a pretty funny scene in which the Doctor matirealises his console inside a rubbish tip after making a "So long suckers!" speech to the Brigadier.
Much later on, Rusty T. Dollopings would awaken one morning, having watched Inferno and the secret original copies of The Tenth Planet all Showruiners get access to while in the midst of a cocaine psychosis, and decide to make a sequel to the conflated (and conflagrated, ah ha, do you see what I did there) mega-episode. Thus would be formed the renowned and beloved NuWho episode Rise of the Cybermen.