The Brigadier asks the Doctor to investigate the disappearance of several scientists, only for him to find they have been abducted back in time.

The Doctor tracks the missing scientists to Irongron's castle, where Linx is using them to repair his spaceship and construct advanced weapons for Irongron.

The Doctor escapes the castle with Sarah and Hal and must persuade Sir Edward to trust him before Irongron launches an attack on them.

The Doctor attempts to return the scientists to their own time before Linx tries to use his spaceship and destroys the entire castle.

The Doctor and Sarah return to London in the present day only to find the city strangely deserted, while nearby UNIT are dealing with a series of monster appearances.

The Doctor and Sarah returns to present-day Earth, where they find London has been evacuated, and Dinosaurs are on the loose and they are mistaken for looters. Assisting U.N.I.T in the emergency, The Doctor and Sarah discovers corrupt politician Sir Charles Grover MP, renegade scientists Butler and Professor Whitaker and military officer General Finch are using a time...

Yates sabotages the Doctor's equipment to stop him finding the location of Whitaker's base but then the tyrannosaur escapes, placing Sarah in danger.

Sarah attempts to find a way off the spaceship while the Doctor tries to track down the source of the time displacements.

The Doctor has been framed as the monster maker by Finch and is on the run from the army, while Sarah attempts to alert UNIT to what Grover is up to.

The Doctor is rescued from Finch by the Brigadier and Benton and tries to persuade them to stop Grover before millions of people are erased from history.

As the TARDIS heads to the paradise planet Florana where the Doctor and Sarah go for a holiday, the TARDIS goes off-course and arrives on the barren planet Exxilon, where the TARDIS is losing power. The Doctor and Sarah finds a group of humans and Daleks are searching for parrinium, a mineral which is the only antidote to a space plague. Both parties encounter the nat...

The Doctor and the MSC crew join forces with the Daleks to mine the parrinium, only to come under attack from the Exxilons.

The Doctor and Sarah meet up with Bellal, who helps them escape from the Daleks and explains the origin of the City.

The Doctor and Bellal continue to penetrate the City's defences while Sarah and Jill try to stop the Daleks leaving with the parrinium.

Returning to the medieval planet Peladon (50 years after "The Curse of Peladon") The Doctor and Sarah find King Peladon's daughter Queen Thalira has inherited the throne and the galactic Federation is at war with Galaxy Five and The Federation requires the mineral Trisilicate that will end the war. However, the miners led by the mad rebel Ettis are rebelling and refus...

The Doctor is rescued by Gebek, prompting him to try and help the miners, but his advice results in Ettis launching another attack on the armoury.

The Doctor and Sarah pacify Aggedor and the Doctor encourages the Queen to make peace with the miners, but Ortron soon has him under arrest again.

The Ice Warriors take control of the planet and force the miners to return to work but Ettis takes the opportunity to try and destroy the citadel.

Sarah and Alpha Centauri decide to try and alert the Federation to what the Ice Warriors are up to but first they have to escape from the throne room.

The Doctor turns the Aggedor spirit against the Ice Warriors to aid the Peladonians in their battle but Eckersley attacks him with the security system.

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.