The Tardis materializes on what appears to be an Edwardian racing yacht.

Turlough tries to commit suicide to escape the influence of the Black Guardian.

The Doctor discovers that the captain of the pirate ship is actually a concentrated beam of mental energy.

The Doctor manages to eject Wrack and pilot her vessel to victory.

The Doctor connects the unexplained disappearance of North Sea oil rigs to an alien race inhabiting Loch Ness. With Tom Baker.

The Doctor is brought before the chief Sea Devil and counsels peace.

Under duress, the Doctor helps the Master repair a unit that may revive Sea Devils globally.

The Doctor is mistaken for Earth's representative at a meeting of the Galactic Federation.

The Doctor faces a royal beast.

Jo receives a royal proposal.

The Doctor battles the beast.

The Doctor finds the original space probe, but not the astronauts.

Aboard the alien spacecraft, the Doctor is given an ultimatum: return the Martian ambassadors unharmed or Earth will be destroyed.

Gen. Carrington kidnaps the Martians and plans to attack the alien spacecraft.

Scientists drill through the Earth's crust in search of new energy sources.

Professor Stahlman refuses to shut down the drilling project, but does cut the power to the Tardis.

The Doctor lands in a parallel world.

The Doctor is trapped on a doomed planet.

The drill site blows up, releasing gases that threaten Earth.

As the doomed world explodes, the Brigadier and Liz try to force the Doctor to take them to the parallel world.

The Doctor returns to the first world and finds that it may share the same fate.