Day 409: Planet of Evil Part 4

The key driving force behind this story is one of an anti-matter monster which is rather annoyed that anti-matter is being taken from them. The Doctor resolves to ensure that all anti-matter is handed back, however there is a scientist, Professor Sorenson, who disagrees with this and sneaks anti-matter aboard the spaceship. Later, in scenes reminiscent of Inferno, we see the Professor turn into a monster, nicknamed Anti-Man by the Doctor, reflecting the mania with which he proceeded to keep the anti-matter in an attempt to find an alternate energy source.

But there's more to it than just that. Sorenson is fully aware that he is turning into a monster and tries to keep it under control with a vaccine. The Doctor then informs him that the vaccine will no longer work, and that Anti-Man will soon take full control over Sorenson. So in a harrowing scene, we see Sorenson lie down and prepare to be ejected into space. His hand hovers over the switch to eject himself, but we see that the hand has already changed into something monstrous. In a way, the Professor does die at that point. But it's not because he was ejected into the cold vacuum of space, instead it is because the monster has taken over. And whilst all turns out well by the end of the story, and the Professor regains his senses, this singular moment of horror remains one of the most truly disturbing scenes in Doctor Who.