In 2526, 8 Earth paleontologists and geologist were investigating a fossil find in a newly discovered case when 7 of them disappear. The only one who seems to have got out is Professor Kyle. She accompanies Lt. Scott and his troop of soldiers into the unmapped caves to see if they can find her colleagues. What they find however is the Doctor and his traveling companions Nyssa, Adric and Tegan who have also just arrived in the TARDIS. They're near the location where the scientific expedition was attacked and Scott suspects the Doctor. There are others in the in the subterranean structures however.
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Winner of the Doctor Who magazine best Story in their Season Poll. See more
When the troopers are in the caves, the two dark figures in background walk past (to the right) and one of the troopers stops and turns around. As he does this the shadow of a crewmember can be briefly seen on the left wall. This is not the dark figure's shadow because they have already walked past. See more
[one of the Androids focuses its gaze on the Doctor and the image is transferred elsewhere to a visual console that the Cybermen are watching
Destroy them! Destroy them at once!
Referenced in Was Doctor Who Rubbish?