The Doctor and Romana prevent the Marshal from concluding his plan and discover what the last segment of the Key to Time actually is. They then encounter both the Black Guardian and The White Guardian in their effort to conclude the mission given to them by the White Guardian.

The Doctor with Drax's help, escape from their prison and work to stop The Shadows plan. The Shadow uses Astra to further the Black Guardians plot to obtain the Key to Time.

K-9 communicates with the leader of the Zeos world and the Doctor attempts to keep the leader from completing it's plan. The Doctor and companions discover the unknown world that is between Atrios and Zeos.

While faithful K-9 awaits the return of the Doctor and those with him, he is taken prisoner by The Shadow. With The Marshal determined to attack Zeos, the Doctor has to put a halt to his plan in order to save Atrios and billions of lives.

When the Doctor and Romana work to escape they Marshal, they not only discover that their TARDIS has been buried underneath a pile of rubble from a recent Zeos attack, but also they discover someone who may be trapped and kidnapped by a unknown source.

In their search for the final segment of the 'Key To Time', the Doctor and Romana land the TARDIS on the world of Atrios who is at war with it's neighboring planet Zeos. Upon avoiding a missile attack right before landing, the Doctor and Time Lady Romana are then mistaken for spys from Zeos by the Marshall.

The Doctor races to stop Thawn from destroying the Swampie settlement and then works to destroy Kroll once and for all.

The Doctor, Romana and Rohm-Dutt are sentenced to death by the Swampies while the refinery crew try to work out a way to destroy Kroll.

The Doctor rescues Romana from the Swampies but is horrified to hear that Kroll has awoken.

The Doctor and Romana land on the moon Delta III, home to the green-skinned Swampies and a small group of human colonists. Soon after arriving, Romana is taken by the Swampies who wish to sacrifice her to the mysterious squid-like Kroll.

After the Doctor escapes Grendel's trap, plans are made to rescue both the Prince and Strella. Count Grendel continues to finalize his plan to take over the kingship.

The confirmation of the King has been put on hold, and the Doctor works on repairing the android of the future king in time. Count Grendal meanwhile, having had his plans interrupted works to stop the confirmation so he can become king in the Princes place.

Romana is being held prisoner by Count Grendal, the Prince and his men along with the Doctor are drugged when they toast to the king after the Doctor has fixed the Prince's android. He is then accused of being involved in the Princes disappearance. They then have to figure out a plan to still get the android crowned as the Prince has vanished while the men were unconscious.

The Doctor and Romana are now searching for the 3rd segment of the Key to Time. Landing on the world of Tara, the Doctor decides to send Romana off in search of the 3rd segment while he takes a break and does some fishing.

The Doctor convinces the Megara to give Vivien Fay a truth test while playing for time so Romana can get back to Earth and find evidence against Vivien.

The Doctor transfers to Hyperspace to save Romana from her imprisonment and has a run in with the Megara Justice machines during his search.

Romana ends up hanging on the side of a cliff while the Doctor is captured by Druid pagan worshipers. The Doctor and the Professor then go on a search for Romana after finding her shoes.

In their search for the 3rd segment of the key to time, the Doctor and Romana land on Earth at a Stonehenge type site where worshipers are engaged in their practice and people are being killed by unknown causes. While en route the Doctor and Romana hear a strange voice that says 'Beware the Black Guardian".

The Mentiads with the help of the Doctor work to foil Queen Xanxia's plan to regain a body and destroy Earth in the process.

The Doctor takes Romana down to investigate the planets mines and gets unexpected help when the Captains guards show up to confront them.

After the Mentiads knock the Doctor out, he discovers that Romana has been taken to the planets bridge. He then travels to the bridge to help her and ends up being forced to help repair the engines.

In seeking the second segment of the Key to Time, the TARDIS heads for an icy world but lands on a populated planet that shouldn't be there.

The Doctor returns to the city to keep an eye on the Graff, leaving Romana, K9 and Garron to search for Unstoffe and the first segment. However, Garron double crosses them and steals the tracer.

The Graff takes the Doctor, Romana and Garron prisoner and then sets about trying to track down Unstoffe and the jethryk.

The Doctor and Romana investigate Garron's activities but this results in the Graff believing they are working together.

The Guardian of Time gives the Doctor a difficult task,and a new assistant. Together they must search for the six segments of the Key to Time, to prevent the Universe from being plunged into eternal chaos. On their mission, the Doctor and Romana travel to the planet Ribos where the first segment of the key is protected by the monstrous Shrivenzale.