The Doctor and Peri crash-land on the planet Serenity, a former member of the Traken Union, after a group of nearby Melkur force them onto the planet. They're soon separated when the local inhabitants capture the Doctor, and Peri is left alone with some shady thieves who want to enter the Tomb of Malador, home to one of the most evillest beings of the local star systems, and currently in a coma. Naturally, one of them awakens the monster, and soon the Doctor has a new formidable foe to stop from conquering the galaxy.
- Brown Note: The Lament of the Melkur.
- Continuity Nod: Traken's destruction is mentioned.
- Heroic Sacrifice: Ebbko.
- Kangaroo Court: The Guardians hold one for the Doctor, then Mura holds one for the Guardians.
- Non-Indicative Name: The Doctor points out prior to landing that Serenity is not really peaceful due to the totalitarian government.
- The Quisling: Auga almost immediately defects to Malador's side, despite unintentionally resurrecting him.
- Reverse the Polarity: Not of the Neutron flow as usual, but of the state of grace surrounding the planet to broadcast the Melkur activation sound.
- Sequel Episode: To The Keeper of Traken.
- Well-Intentioned Extremist: Poor Auga didn't realise that destroying Prophecy would resurrect an ancient evil.
- You Have Outlived Your Usefulness: Malador enjoys dangling this threat over Auga's head to keep him in line.