The Power of Kroll


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The Power of Kroll

Serial Code


First Transmitted

23 December 1978

Final Ratings






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Regular Cast

Tom Baker (Doctor Who), Mary Tamm (Romana), John Leeson (K9)

Guest Cast

Neil McCarthy (Thawn), John Abineri (Ranquin), Philip Madoc (Fenner), Glyn Owen (Rohm-Dutt) [1-3], Carl Rigg (Varlik), Frank Jarvis (Skart), John Leeson (Dugeen), Grahame Mallard (Harg) [1-2]*, Terry Walsh (Mensch).


Written by David Fisher
Directed by Michael Hayes
Produced by Graham Williams


The Doctor, Romana and K9 continue their search for the six disguised segments that make up the powerful Key to Time. The TARDIS brings The Doctor and Romana to Delta 3, the third moon of the planet Delta Magna. Romana is captured by the Swampies, the original inhabitants of Delta Magna, displaced from their home world by human colonists. They intend to sacrifice Romana to their god, the mighty Kroll. The Doctor’s search for his companion brings him to a massive refinery in the middle of the swamp, which is extracting protein from under the water to feed the people of Delta Magna.

The Doctor is mistaken for Rohm-Dutt, an amoral gun-runner who is supplying the Swampies with weapons to aid them in their plan to attack the refinery and force the workers to leave Delta 3. The Doctor escapes the refinery in time to rescue Romana from the sacrificial altar, discovering in the process that Kroll is just a myth, a story to frighten children. They resolve to find the Fifth Segment and leave the moon, avoiding the intrigues of the refinery workers and the attentions of the fanatical Swampies. However, all is not as it initially seems.

What is stirring on the floor of the swamp and can the instruments on the refinery really be correct in saying that it is five miles across? The Doctor realises that Kroll is more than a mere legend and its centuries-long slumber has been disturbed by the refinery. Now it is awake, the time-travellers find that it is very large, and very hungry…


  • Working titles for this story included Moon of Death, Horror of the Swamp and The Shield of Time. It should be noted that this final working title was part of a short-lived idea that all stories in Season 16 were going to be entitled The (Something) of Time, with the last story (which eventually became The Armageddon Factor) named simply The Key to Time.
  • This story features a guest appearance by Philip Madoc. Madoc had been invited to play Thawn, but the invitation was withdrawn because Neil McCarthy had already accepted the role. He agreed to play the part of Fenner when Alan Browning, who was slated to play Fenner, fell ill before the start of production.
    John Leeson, best known as the voice of K9, appears in this episode as Dugeen, in part because the location of the story rendered the use of K9 unfeasible. This marks Leeson’s only on-screen appearance in Doctor Who. Coincidentally, the end of the previous story, The Androids of Tara &mdash, which sees K9 stranded in a rowing boat in the middle of Castle Gracht’s moat &mdash, offered a practical demonstration of why water and K9 did not mix.
  • The BBC’s Head of Serials, Graeme MacDonald, was so unimpressed by the set designs in this story that he ordered that designer Don Giles was never to work on the series again. By coincidence, episode 3 includes a line of dialogue in which The Doctor criticises the decor of the Swampies’ execution chamber and recommends its architect be fired.
  • The episodes of this serial are noticeably shorter than average. While it was normal at the time for individual episodes to fluctuate between twenty-three and twenty-five minute, the episodes of this serial clocked in as little as just over twenty-one minutes. In addition, Episodes 3 and 4 begin with longer-than-usual reprises of the events leading up to the preceding cliffhangers, both clocking in at close to ninety seconds each. The final running time for the whole serial is 90 minutes, as is noted by the DVD of this story.
  • The moon is never named on-screen. In his novelisation of the story, Terrance Dicks named the moon Delta III.
  • Tom Baker was credits as ‘Fourth Doctor‘ in Radio Times,as opposed to the usual ‘Dr. Who’. The use of this billing had previously occurred with Image of the Fendahl. In the closing titles, the term The Doctor would not be used until Castrovalva in 1982.
  • The sacrificial stone is referred to as the “Stone of Blood”. An earlier story in this season was called The Stones of Blood.
  • The Fourth Doctor, talking to himself before his final encounter with Kroll, says he is seven hundred sixty years old. This suggests he is either rounding up (as his age was given as seven hundred fifty-nine in The Ribos Operation) or he’s had a birthday since beginning the Key to Time mission. A birthday scene was originally planned for The Stones of Blood but dropped by Graham Williams, who considered it “too self-indulgent”, as was noted in Doctor Who Magazine.
  • The green make-up for the Swampies was specially ordered from Germany. Unfortunately for the actors, the remover wasn’t and so they either had to undergo chemical showers at RAF Bentwaters or have their skin scoured in the hotel. Many had a green tinge to their skin for weeks
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