The Doctor, Jamie and Zoe realise they have arrived in the trenches of the First World War, where the sinister General Smythe accuses them of espionage.

The Doctor and Liz are summoned to the Wenley Moor Research Centre by the Brigadier, after several staff members suffer nervous breakdowns.

The Doctor attempts to convince people there are monsters in the caves, prompting Major Baker to start shooting at a reptile man.

The Silurians contact Quinn for help in retrieving the creature while the Doctor and the Brigadier organise a search of the moors.

With Quinn dead, the Brigadier decides to take an armed party into the caves, prompting the Doctor to contact the Silurians himself.

Worried about the Old Silurian's growing friendship with the Doctor, the Young Silurian has the scientist infect Baker with a virus and then release him.

While the Doctor and Liz try to find a cure to the virus spread by Baker, the Young Silurian kills the Old Silurian and takes control of his people.

While Liz distributes the cure to the virus, the Doctor discovers the Silurians now plan to wipe out humanity by destroying the Van Allen Belt.

UNIT retrieve the returned Recovery 7 but then Carrington hijacks it while the Doctor and Liz try to decode the signal he sent.

Carrington is holding the astronauts at a secret location but when he takes the Doctor, Liz and the Brigadier there they find they have been kidnapped.

Liz has been captured by Reegan's men and the Doctor begins to suspect Taltalian is more involved than he appeared.

The Doctor decides to take Recovery 7 back into space to search for the missing astronauts but Reegan sabotages the launch.

The Doctor speaks with the alien captain and learns the astronauts sent to Earth were ambassadors. However, before he can alert the authorities he is kidnapped by Reegan.

Carrington is planning to expose the aliens on live television and call for an interplanetary war and the Brigadier must rescue the Doctor and Liz in time to stop him.

The Time Lords take control of the TARDIS and the Doctor and Jo arrive on an Earth Colony in the 25th century, where a ruthless mining company are using a dinosaur-like creature to force the colonists to leave the planet.

The Doctor discovers an Interplanetary Mining Corporation ship has landed on the planet in order to mine its duralinium, while Norton begins causing trouble at the colony.

The Doctor makes it back to the colony and warns Ashe what Dent is up to but when Jo and Winton try to find proof they are captured.

The Doctor descends into the Primitive city to try and find Jo while the colonists receive a visit from the Adjudicator.

The Master offers to help the colonists in exchange for information on the Primitive city and forces the Doctor to act as a guide by taking Jo hostage.

The Doctor and the Master are taken into the Primitive city, where the Master hopes to find the doomsday weapon, while Dent forces the colonists to leave the planet even though their ship is likely to explode.

The Doctor and Jo visit the Master at his island prison where the Doctor becomes curious about a number of ships sinking in the area.

The Doctor and Jo are trapped on the fort by a Sea Devil while the Master convinces Trenchard to help him steal some electronic components.

The Doctor is held prisoner by Trenchard while the Master attempts to contact the Sea Devils.

The Sea Devils attack the island prison and rescue the Master, prompting the Doctor to venture underwater to try and contact them.

The Doctor is taken to the Sea Devils' underwater colony where he tries to make peace with the creatures, only for the navy to attack the base.

The Sea Devils take over the naval base and the Doctor is forced to help the Master find a way to revive their colony.

The Doctor and Jo land on a spaceship in the far future as it is attacked by Ogrons, which the human crew see as Draconians. The Doctor and Jo are taken to Earth as spies.

The Doctor and Jo are taken to Earth, where both humans and Draconians believe them to be a spy for the other side.

The Doctor is sentenced to life imprisonment at a lunar penal colony while Jo encounters an old enemy.

The Master rescues the Doctor from the lunar penal colony, aiming to take him and Jo to the Ogrons' planet, and the Doctor's attempt to escape leaves him stranded in space.

The Doctor, Jo and the Master are taken to Draconia, where the Doctor tries to convince the Draconians of the truth.

The Doctor, Williams and the Draconian Prince head to the Ogrons' planet to find evidence of the Master's actions but the Master tricks Jo into leading them into a trap.

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 attempts to solve the mystery of the monster invasion. His first move - the capture of a dinosaur.

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.