Dragonfire

"They will have no past, no future, no will of their own.  No purpose except to obey me.  To them I shall be invincible.  My power shall be absolute!"

Iceworld.  An intergalactic trading post, ruled by the power-hungry Kane.   Now his dream of total power is near to realization with his acquisition of a band of mercenaries from the infamous Glitz in part payment for his debts.  For "Cryosleep" will render the men utterly in his power. 

Meanwhile, Glitz still owes the balance of the debt and looks to Iceworld’s mythical dragon and the Dragonfire-the treasure it reputedly guards-to solve his problems at last.  Intrigued by the legend of the Dragonfire, the Doctor, Mel and young Earth girl, Ace, accompany Glitz-unaware that they are being followed by Kane’s mercenaries.  For the psychotic ruler believes that with Dragonfire in his possession he can avenge the rulers of his home-planet who banished his long-dead partner 3,000 years ago.  And so it seems that beneath Iceworld’s superficial civility lies a frozen core of corruption and the Doctor has embarked on something far more sinister than a mere treasure hunt…

• A shaky season ends on an upbeat note with "Dragonfire."  It is also worth noting that this story marks the 150th adventure of Doctor Who.

• One of the least liked companions among fandom, Melanie, leaves at the end of this story.  Ironically, she is replaced by one of the most popular companions among fandom, Ace.  Surprisingly, Mel's departure is handled in a very touching and sincere way.

• By the time this story was being written it was known that companion Mel (Bonnie Langford) was preparing to leave at the end of the season.  Producer John Nathan-Turner took the unusual step of instructing both the writer of this story and that of "Delta and the Bannermen" to prepare a character who could join the Doctor at the end of the story.  Ace was developed as a possible companion for this story, while Ray would be the one for "Delta and the Bannermen."

• Sabalom Glitz makes a return from the previous season story "Trial of a Time Lord."  Glitz was not in the original draft of this story, but rather a pirate called Razorback.  Glitz was added at the request of producer John Nathan-Turner.

• Also of note is Edward Peel who puts in a very chilling (no pun intended) performance as Kane, the villain of the month.