INFERNO
Taking advantage of a scientific project's nuclear reactor, the Doctor attempts to fix his TARDIS. The project involves drilling through the crust of the earth to access stores of gas underneath, providing cheap and plentiful energy. The drilling becomes problematic when it brings up a green goo that turns whoever touches it into a green monster. Realizing that this is symptomatic of a more serious problem, i.e. the destruction of the entire earth, the Doctor tries to warn his friends. They ignore him and he storms off to his TARDIS, and tries to take off ...
He finds himself in a parallel dimension, his malfunctioning TARDIS slipping him sideways in time. In this universe the Nazis have won the war and his parallel friends are in fact his enemies and suspect that he is a dangerous spy. He tries to stop the project there, but is unable to and once the end of the world is imminent, convinces the crew to help him get back to his own world. Once there he is just barely able to stop the project in time.
I love this serial for the parallel world. Nick Courtney, Caroline John, and John Levine are terrific as evil versions of their regular characters. The story itself is a little silly. The Primords (green monsters) are ridiculous and don't make much sense (I know there needed to be monsters for the kiddies, but green werewolves? Why not red lava monsters?) and the outcome is a little too extreme - why the destruction of the whole world? Why not just Britain? The special edition DVD gives us a lot of behind-the-scenes information and the original screenplay made the parallel world more alien. The months there had different names and were 50 days each, and English spelling was more primitive. I liked the characterizations of the final product better.
The one real failure of the serial is in the last episode. After what he learned in the parallel world, his friends still ignore him until the head of the project turns into a Primoid. His foray into the parallel world is pointless, other than to show the consequences of the Doctor failing. Really, the strength of this story rests on the performances of the actors rather than the actual plot, but for that, it is still my favorite serial.