question of the day: What are the most frightening episodes of ‘Doctor Who’?

I found a lot of the gothic Tom Baker stories pretty frightening: “The Seeds of Doom” was pretty creepy, with its body-conscious horror (the villain gets transformed into an alien plant). I still find something really unsettling about the immortals in the Peter Davison story “Enlightenment”: though they look entirely human, they have an eerie kind of calm about them that makes them feel way more alien than most of the guys in rubber suits have ever been.