The Doctor anf Sarah

After retiring from UNIT, under medical grounds, Captain Mike Yates is attending a meditation centre where he becomes suspicious of the activities of Lupton, Barnes, Land, Keaver and Moss, who seem to be summoning powers through their chanting. He arranges for Sarah Jane Smith to come along, in her capacity as a journalist for the Metropolitan magazine, to try and uncover what is happening.

On arriving at the centre, after a hair-raising journey from the station, Sarah talks with Cho-je, the centre's Tibetan guide, and meets Lupton. After giving the impression they have left Mike Yates and Sarah return to the centre and hide in the cellar before Lupton's group arrive and start chanting. To Sarah's horror, a giant spider appears before them and jumps on Lupton's back and then vanishes.

At UNIT’s HQ a Professor Clegg, a stage magician who seems to possess genuine powers, demonstrates telekinesis to The Doctor and The Brigadier. When given The Doctor's sonic screwdriver he 'sees' Drashigs and when Sergeant Benton arrives with a package from the Amazon, Professor Clegg correctly identifies its contents as the blue Metebelis crystal given to The Doctor’s former companion Jo Grant as a wedding present. However, while the others are distracted, Professor Clegg is killed when he looks into the crystal.

The Doctor

When Sarah returns to the UNIT HQ and tells The Doctor what happened and mentions the giant spider, The Doctor is immediately interested as spiders were the last thing seen by Professor Clegg before he died. Unknown to The Doctor because of Professor Clegg’s actions Lupton has become aware of the Metebelis crystal and so he arrives at UNIT HQ in search of the crystal, as instructed by the invisible spider still on his back. He knocks out a soldier with powers given to him by the spider and, on seeing the crystal in the UNIT laboratory, he transports it to his hands. Witnessing this The Doctor, Sarah, The Brigadier and Sergeant Benton chase after him. But after a chase involving The Doctor's new space-car, Bessie, an autogyro, a speedboat and a hovercraft, The Doctor catches up with Lupton only to then watch him vanish.

Lupton materialises back at the meditation centre but is unaware that he is being watched by a resident, the naïve Tommy, who, on seeing the crystal, is compelled to steal it. When Lupton and Barnes become distracted, with their discussion on what to do next, Tommy takes it without either of them noticing. The Doctor then arrives, with Sarah, to see Cho-je. Tommy tries to give Sarah the crystal as a present but she is more interested in listening into Lupton planning to perform another ceremony in the cellar on his own. After sending Tommy to alert The Doctor she follows Lupton to the cellar and then watches as he vanishes. Just as The Doctor rushes into the cellar she vanishes as well and reappears on Metebelis 3.

The Metebelis Crystal

There, in a human village, she meets Nesca and Sabor who help her to hide in a hut when the Queen of the eight legs arrives, with her guards, to take Arak away as he had earlier killed a guard. But Sarah is spotted and is held by the Queen's guards. The Doctor then arrives in the TARDIS and fights with the guards. In the confusion, Sarah manages to escape and is again hidden by Nesca. The Doctor is knocked out and, when the Queen has gone, he is taken into Nesca's hut. He is very weak and is only just able to instruct Sarah to fetch a machine from the TARDIS which will help him. She gets the machine, but is captured by guards and taken away. When Sarah does not return, and with The Doctor becoming worse, Arak retrieves the machine from by the TARDIS, where Sarah had left it when she was taken away, and The Doctor uses it to save his own life.

When The Doctor recovers Arak explains to him that the spiders came to Metebelis 3 with the humans on a spaceship 433 years ago. The spiders were blown onto the mountains where the blue crystals enlarged their minds and bodies until they were powerful enough to enslave the human population. The Doctor goes to the spiders' city but is captured and placed in their 'larder' with Sarah. Sarah is released and taken before the Queen spider. She tells Sarah that she disagrees with the spider’s plan to invade Earth and wants Sarah to help her. This Sarah agrees to do. Meanwhile The Doctor manages to free himself from the 'larder' and, on hearing Sarah calling to him, he follows her voice to a cave of blue crystal. There he discovers the Great One, the ruler of all the spiders, who has lured him to her because she wants The Doctor to return to Earth and fetch the blue crystal for her.

Back on Earth, Mike Yates manages to persuade Barnes to reopen the link in case Lupton is waiting for this to return to Earth. They meet in the cellar and start chanting. However, they are unaware of the Scout spiders appearing in the shadows behind them. Suddenly Cho-je, having been told by Tommy of what has been happening, enters the cellar but a spider blasts him and Mike Yates before the other spiders attach themselves to Barnes, Moss, Land and Keaver. Tommy though is able to hurry away and sets off to warn the Abbot, K'anpo Rimpoche.

A Spider of Metebelis Three

Meanwhile back on Metebelis 3, The Doctor finds Sarah and she transports him back to the village where they enter the TARDIS and return to Earth. On arriving back at the meditation centre they are attacked by the spider controlled humans but The Doctor has a Metebelis stone, which he discovered earlier can be used against the spiders, which deflects the blasts. They then meet Tommy who takes them to see the Abbot. As soon as The Doctor enters the Abbot’s room he recognises him as his old Time Lord tutor. With Tommy holding the others off at the door, K'anpo brings out the crystal. As soon as Sarah sees it she demands he hand it over to her – making The Doctor realise that she is being controlled by the Queen spider. The Doctor uses the crystal to free Sarah from the spider's influence and it falls from her back and dies. K'anpo then reveals that Cho-je is a projection of himself. He also makes The Doctor realise that all the recent events are the results of taking the crystal from Metebelis 3 in the first place, and that he must now face his fear, and probable death, by returning to the cave of the Great One to give back the crystal.

Outside the Abbot’s room the spiders summon up more power and blast Tommy again just as Mike Yates arrives - who also takes a blast. This allows Barnes and the others to finally enter K'anpo's room and to attack the Abbot who then regenerates into the form of Cho-je. At the same time The Doctor vanishes and reappears in the cellar where he enters the TARDIS which takes him back to Metebelis 3. There he meets Arak and Tuar, now are under the spiders' influence, who take him to the spider's council chamber. The Doctor tells the giant spiders that he is going to return the crystal to the Great One. But as The Doctor goes to leave Lupton tries to stop him but is killed by a blast from the spiders.

When The Doctor arrives at the cave of the Great One, and confronts the giant spider, she takes the crystal from him so as to complete her 'web of power' - believing that it will increase her mental powers to infinity. The Doctor though realises that she has created a positive feedback circuit that will eventually destroy the Great One's mind. The Doctor though is getting weaker from the high level of radiation in the cave of the Great One. He staggers from the chamber and just manages to return to the TARDIS as all the spiders die so releasing the humans from the spiders' mental domination. As the TARDIS dematerialises the mountain explodes, destroying the Great One.

Back on Earth three weeks have passed, since The Doctor left, and Sarah is at UNIT HQ with The Brigadier wondering if they will ever see The Doctor again when the TARDIS appears. Apparently The Doctor got lost in the time vortex and the TARDIS has brought him home. As he exits from his time-machine he collapses on the floor and apparently dies. However, Cho-je appears and tells The Brigadier and Sarah that he will assist The Doctor's regeneration and so before their eyes The Doctor's appearance changes.