The Third Doctor has developed an interest in psychic ability, but his testing of a clairvoyant called Professor Clegg backfires when his subject has a heart attack. It is triggered when Clegg comes into contact with a blue crystal from Metebelis Three (sent back from the Amazon by Jo Grant), which caused him to see the image of deadly spiders. Sarah returns from the retreat and she and the Doctor swap spider tales. Meanwhile, Lupton has also arrived at UNIT HQ and steals the crystal from the Doctor’s laboratory. A multi-vehicle chase ensues which Lupton escapes by teleporting himself back to the monastery. Once there, the spider reveals that it is plotting against some of its sisters back on Metebelis Three. The spiders and the crystal originate from the same blue planet in the Acteon Galaxy the Doctor last visited during "The Green Death".