The Doctor receives a mysterious package from his old companion, Jo Grant. Sarah joins Mike Yates to investigate sinister events at a Buddhist meditation centre.
Lupton, now under the control of a giant spider, infiltrates UNIT HQ and steals the Metebelis crystal. But the Doctor is unwilling to give it up so easily and a chase begins.
With the Doctor in a coma, his only hope of survival lies with a device inside the TARDIS. Sarah is captured by the spiders and is held prisoner in their larder.
Following Lupton, Sarah is transported to Metebelis 3 where she is captured by the human villagers. The Doctor uses the TARDIS to follow Sarah, but the spiders are waiting.
Sarah makes a bargain with the Queen Spider and returns to Earth with the Doctor in the TARDIS.There they meet K'anpo,the Doctor's Time Lord guru who has the Metebelis crystal.
The Doctor takes the blue crystal and returns to Metebelis 3 where he must face the spider ruler, the Great One. But it is an encounter that triggers his second regeneration...