Fear of the Dark (5th Doctor)

In the year 2382 archaeologists land on Akoshemon's only moon, searching for evidence of the planet's infamous past. But when the Doctor, Tegan and Nyssa are drawn into the lunar caverns they find more than a team of academics -- and help uncover much more than ancient history. Something is lying in wait, deep inside the labyrinth of caves: something that remembers the spiral of war, pestilence and deprivation that ruined Akoshemon. Something that rejoiced in every kind of horror and destruction. An age-old terror is about to be reborn. But what is the hideous secret of the Bloodhunter? And why does Nyssa feel that her thoughts are no longer her own? Forced to confront his own worst fears, even the Doctor will be pushed to breaking point -- and beyond.