The Doctor discovers Polly and Ben aboard the TARDIS shortly before the ship arrives in 17th century Cornwall, where the local churchwarden gives the Doctor a cryptic message shortly before being murdered.
Pike is convinced that the Doctor knows the location of Avery's treasure while Polly and Ben try to convince the locals they were not responsible for Longfoot's murder.
Polly and Ben are placed in the custody of Blake, who reveals he also has his suspicions about the Squire, while the Doctor and Kewper are forced to team up to escape from Pike's ship.
In December 1986, a new planet appears in the Solar System which turns out to be a long-lost twin of Earth's named Mondas. Its inhabitants are the Cybermen.
The Cybermen take over the base again, apparently to stop the humans using the Z-Bomb, but then the Doctor realises they intend to use it themselves to destroy Earth.
The Doctor, Polly and Ben arrive in 1746, in the aftermath of the Battle of Culloden, and are captured by a group of Highlanders shortly before they themselves are captured by redcoats.
Ben manages to join up with the Doctor, Polly and Kirsty and together they work to free the Highlanders from Trask's ship before Grey sells them into slavery.
The TARDIS materialises on a deserted beach where the Doctor and his friends are captured by primitive warriors and taken to the fabled city of Atlantis.
While Ara tries to save Polly from being turned into a Fish Person and Ben and Jamie try to escape from the mines, the Doctor discovers the full extent of Zaroff's plans.
The TARDIS arrives on the Moon in the year 2070. When Jamie is injured, the other travellers are forced to seek the help of a moonbase afflicted with a space plague.
The Doctor and his friends attempt to convince the Moonbase crew that the Cybermen are responsible for the disappearances and find a cure for the plague.
With the Cybermen preparing to launch a full attack, the Doctor and his friends must keep the Moonbase and the Gravitron out of their hands until help arrives from Earth.
The TARDIS arrives at a holiday camp company with the crew worried by a prediction of giant crabs and the Doctor becomes interested in the apparent madman Medok's stories of creatures that roam the colony at night.
When Spencer attempts to kill them, the Doctor, Jamie and Sam become convinced Chameleon Tours are hiding something and Sam decides to book a ticket on one of their flights.
Jamie finds himself aboard the Chameleons' satellite and meets their Director while the Doctor forces the Chameleon Meadows to tell him the aliens' plans.
The Doctor and Pinto are captured by the Chameleons but the Doctor manages to use their dependence on their human originals to create dissent in their ranks.
