Earth, the near future. When an archaological dig at the village of Devil's End goes disastrously wrong, an ancient power begins to revive. Can even the Doctor withstand the power of the Daemons? And just what is the local vicar up to in his spare time?

With the Doctor frozen by the energy release from the barrow, Jo calls Yates and Benton for help, but when the Brigadier tries to join them he finds the village surrounded by a heat barrier.

The Doctor explains to his friends that the Master is trying to gain the power of the last of the Daemons, a race who influenced Earth's development, while the Master brings the rest of the village under his control.

The Master orders Bert to set a trap for the Doctor at the village while a concussed Jo makes for the cavern.

The Master decides to sacrifice Jo to Azal and when the Doctor and his friends try to intervene they come under attack from Bok.

UNIT are invited to observe a demonstration of the new TOMTIT machine, unaware its creator, Professor Thascales, is actually the Master.

The Doctor realises the Master is trying to harness the power of Kronos, last of the Chronovores, but is unaware Percival is harbouring him at the institute.

The Master enlists the help of Krasis to control Kronos while Yates tries to bring the TARDIS to the institute only to come under attack from dangers from the past.

The Master prepares to travel back to Atlantis but the Doctor links his TARDIS to the Master's to try and stop him.

Both TARDISes reach Atlantis, where the Doctor befriends King Dalios while the Master enlists the help of Queen Galleia to try and obtain the crystal of Kronos.

The Doctor enters the labyrinth to try and protect Jo from the minotaur but the Master has seized control of Atlantis and prepares to summon Kronos again.

While the Doctor plans a holiday to Metebelis Three, Jo and the Brigadier are intrigued by a mysterious death at a coal mine in Llanfairfach, which is being blamed on local company Global Chemicals.

The Doctor and the Brigadier attempt to rescue Jo and Bert from the mine but Global Chemicals prove distinctly uncooperative.

The Doctor and Jo manage to escape from the mine with a maggot egg but Stevens is determined to stop them analysing it.

The Brigadier calls in a full UNIT force to deal with the giant maggots while the Doctor infiltrates Global Chemicals to find out what is really going on.

The Doctor manages to escape from BOSS with help from Yates and discovers Cliff has been infected by a giant maggot.

The Doctor attempts to destroy the giant maggots and cure Cliff but the real threat is BOSS, who is poised to take over all the world's computers.

While the Doctor carries out an investigation into ESP, Mike Yates asks Sarah to look into some strange goings on at a meditation centre he's attending.

Lupton forms an alliance with the spider to steal the Doctor's blue crystal, while Sarah and Mike attempt to alert people to what they've seen.

The Doctor and Sarah head to the meditation centre to try and get the crystal back while Lupton prepares to return it to Metebelis Three. But all their plans are disrupted when it is stolen by Tommy.

Sarah is captured by the spiders' guards while the Doctor tries to help Arak and the others strike back against the spiders.

The Doctor escapes from the spiders' larder only to encounter the Great One, while Sarah makes a deal with the Queen Spider.

K'Anpo persuades the Doctor he must face his fear and return the crystal to the Great One.But first they need to get past Barnes and his men.