Written by Robert Holmes
Directed by David Maloney
The TARDIS arrives on the planet of the Gonds, a simple people overseen and educated by the Krotons. The Krotons are crystalline aliens whose ship, the Dynatrope, crashed on the planet thousands of years ago.
The Krotons exist in slurry-like form, requiring the absorption of enough mental energy to reform themselves fully. Periodically, the two most brilliant Gond students are received into the Dynatrope. As far as the Gonds are concerned these two are taken to serve the Krotons, but in truth their mental energy is drained, and their mindless bodies are then taken outside the Dynatrop to be killed.
The Doctor and Zoe take the Krotons' test, and their brains are advanced enough to reanimate the Krotons. However, the Doctor also discovers that make up of the Kortons is based on tellurium, which allows him to destroy them and their ship using a form of sulphuric acid.
Of course, this story is notable for being the first script written for the series by Robert Holmes, who, in short order, would become one of Doctor Who's most consistently brilliant writers and one of its best script editors. Ironically, Holmes script was originally a science fiction serial that had nothing to do with Doctor Who. He pitched it to the BBC as a stand-alone, and though it was rejected, it was suggested he submit it to the Doctor Who office. The then-script editor, Donald Tosh was interested, but nothing happened. Years later, during the chaos of Season Six, assistant script editor Terrance Dicks was scanning the backlog of stories on file and found Holmes' scripts. He and Holmes began working on them on the side, and when yet another serial fell apart in the planning stages, Dicks and Holmes had The Krotons ready to go.
The story is solid, with a nice concept at its core in the idea of a society held back in ignorance by the needs of an alien oppressor. It won't be the last time we see this concept. However, the execution is workmanlike, if uninspired. It has to do with the plotting, which sees a lot of running around and long conversations. There just isn't enough going on to generate the sense of jeopardy. Don't get me wrong, there are some genuinely good moments, including the classic scenes of the Doctor and Zoe taking the Kroton test, and the cliffhanger that sees the Doctor menaced by the Krotons' scanner. But it never quite gels into an exciting adventure. As such, it remains intermittently entertaining, and an easy watch, but never becomes a classic.
Part of the reason may be the design and portrayal of the Krotons themselves. Their voices are decidedly odd, and it's a bold choice to have them sound so regional, but it doesn't really work at all. And their design, while also kind of cool looking, is a bit too clunky to be menacing.
The serial also features the debut of fan-favourite guest actor Philip Madoc. While this isn't one of his classic turns, he still delivers.
All in all, it's an average adventure, but one that shows hints of the brilliance that was to come from Robert Holmes.