The Doctor and Jo discover that an old Welsh mine is infested by maggots that have grown to enormous size.
On the jungle planet of Spiridon, the Doctor and Jo join forces with a group of Thals who have come to defeat a Dalek task force searching for the secret of invisibility.
The TARDIS lands inside an Earth spaceship in the far future where the dominant space powers, Earth and Draconia, are on the brink of war.
The TARDIS lands on a cargo ship in 1926 but when a dinosaur appears and the crew and passengers begin repeating their actions, the Doctor realizes that not all is as it seems.
As gel creatures materialize around UNIT HQ and begin a full scale attack, the Doctor realizes the situation is beyond even him control and sends out a desperate SOS..