When the Silurians were awoken from their hibernation, they discovered that humans had now populated their planet, for they were once the masters of Earth when the humans were only apes. Many Silurians, including Morka, desired to destroy the humans and reclaim the planet. The leader of this group, Okdel, was persuaded by the Doctor that the planet could be shared. However, Morka killed Okdel and became the new leader.
Morka attempted to infect the humans with a fatal disease that quickly spread from person to person. However, this was unsuccessful when the Doctor discovered a cure. Morka's next attempt to wipe out the humans using a reactor was foiled too, when the other Silurians were tricked into returning to their hibernation. Alone, Morka then tried to kill the Doctor but was shot by Brigadier Lethbridge-Stewart several times. Despite this, Morka still clung on to life but was finished off when the Brigadier destroyed the Silurians' base, much to the sadness of the Doctor.