While Tommy is holding off Barnes, K'anpo reveals that he has the crystal. Sarah demands it in the Queen's voice and the massive spider appears on Sarah's back. K'anpo and the Doctor use the crystal to break the Queen's hold on Sarah's mind, killing the spider.
The Doctor suddenly recognizes K'anpo as the hermit who taught him in his youth. K'anpo is a Time Lord and Cho-Je is a projection of him. He tells the Doctor he must face his fear and return the crystal to the Great One, even if it kills him.
Barnes and the others focus their power and unleash one gigantic blast onto Tommy. They can't stop him but hurt Yates, distracting him. They break in just as the Doctor teleports to the cellar. They blast down K'anpo but are unable to catch the Doctor before he takes off.
The Doctor finds Arak and Tuar, who have apparently won. They agree to take him to the Great One's cave but instead bring him to the spider council chamber. They have lost their revolution and are under the spiders' control. The spiders demand the crystal but the Doctor says he will only give it to the Great One. When Lupton tries to take it, the spiders stop him and send the Doctor off to die. After he leaves, Lupton angrily attacks the spiders and is struck down.
K'anpo finds that Mike and Tommy are all right, but he is mortally wounded. He falls and his features fade into those of Cho-Je, who disappears, completing the regeneration.
The Doctor reaches the Cave of Crystal. He enters and confronts a gigantic spider. She tells him that she has built a crystal web that reproduces the pattern of her thoughts. With one last crystal, it will amplify her mind to infinity, taking over the cosmos. But the Doctor realizes that it will kill her and tries to explain this. The insane spider will not listen and levitates the crystal into place.
The cave fills with power. Suddenly, the Great One screams as the power burns up her mind. The Doctor runs out, his heath fading from the radiation. The spiders all die, freeing their human hosts.
Weeks pass on Earth and the Doctor has not returned. Sarah arrives to look for him and the TARDIS lands. The Doctor stumbles out and quickly passes out. K'anpo appears and tells them that the Doctor is dying but will regenerate. As he vanishes, the Doctor's features change.