Season 18 episodes

No   Code   Title                    First Shown  Eps  Exists
-------------------------------------------------------------
110   5N    The Leisure Hive          30 Aug 80    4    all
111   5Q    Meglos                    27 Sep 80    4    all
112   5R    Full Circle               25 Oct 80    4    all
113   5P    State of Decay            22 Nov 80    4    all
114   5S    Warriors' Gate             3 Jan 81    4    all
115   5T    The Keeper of Traken      31 Jan 81    4    all
116   5V    Logopolis                 28 Feb 81    4    all

Notes:

Adric joins as a companion in Full Circle, Romana leaves to stay in E-space at the end of Warrior's Gate, Nyssa appears in The Keeper of Traken and becomes a companion in Logopolis. Tegan becomes a companion in Logopolis when she enters the Tardis believing it to be a Police Box.

Episode Details

The Leisure Hive

The Time Lords arrive at the Leisure Hive, a tourist centre run by the Argolins, a race that is dying after an ancient war with the Foamasi. The elderly leader, Mena, seeks to rejuvenate herself by sponsoring the work of Hardin, an Earth scientist who claims to be able to reverse aging. Hardin's assistant is murdered when he stumbles onto a plot to destroy the Hive, and the Doctor and Romana are suspected of the killing. Can they unmask the true killer and save the Hive?

Meglos

The Doctor receives a message from the planet Tigella, where the Dodecahedron (a huge crystal that powers their entire civilisation) is failing. Before the Doctor can reach Tigella, however, he is imprisoned by Meglos, a malevolent cactus-like creature who impersonates him and steals the Dodecahedron! When the Doctor escapes and finally arrives on Tigella, he is accused of the theft and sentenced to death! Can Romana prove his innocence and retrieve the crystal?

Full Circle

The Doctor and Romana discover that they have arrived in E-space, a totally different dimension from the N-space of the normal Galaxy. Landing on the planet, they discover a mysterious mist is starting to appear. They discover a race of people working towards making a large space ship flight ready, but become suspicious when it appears that they've been working on it for generations.

State of Decay

The Doctor, Romana and Adric arrive on a planet controlled by three mysterious beings who live in a gothic castle. Below the castle is a village and each year several of the villagers are taken to the castle never to be seen again. It becomes apparent that the three beings are vampires who have lived for a thousand years, but what is the darker force that controls them from beneath the castle.

Warriors' Gate

The mysterious appearance of a creature who shares the ability of the Time Lords to sense time as a dimension leads the Doctor, Romana and Adric to a space ship where many of it's kind are held prisoner. Once rulers, they are now kept in slavery as navigators for ships that travel in time by those who they once held captive. Will the Doctor and Romana aid them in their struggle to be free...

The Keeper of Traken

The Doctor is startled when a mysterious old man in a chair appears in the corner of the TARDIS while it is in flight. The man turns out to be the Keeper of the Source, a power that has given the Union of Traken centuries of peace and prosperity. He claims that Traken is in great danger and asks the Doctor to help. Arriving on Traken, the Doctor discovers a statue that seems to have an evil persona of it's own.

Logopolis

Having stolen the body of Tremas of Traken, the Master returns to his old ways and attempts to gain control of the universe by seizing the power of the planet Logopolis. A peaceful planet full of mathematicians working on calculations that hold the fabric of the universe together, the inhabitants of Logopolis soon start dying at the hands of the Master.