These two stories involve Kamelion – a robot who is easily manipulated either for good or evil. The then producer, John Nathan-Turner, saw this revolutionary robot who could talk and move, and thought it would be a great replacement for the much loved companion, K9.
Wrong.
The first story, The King's Demons, is mediocre at best. I'd go so far as to say that it is the worst story I have seen from the Peter Davison era.
Planet of Fire is much better, resolving the story around one companion, Turlough, and introducing another new companion, the bikini-clad Peri, who was quite likeable in this story and the next, but suffered from poor scripts in the next two years alongside Colin Baker's Doctor.
For those who watch ‘The Simpsons’, they'll know how the problem of “Poochie” was solved, and will be aware of the joy it brought to fans. The outcome for Kamelion brought similar joy to every true fan of Doctor Who.
Perhaps worth a watch for “Planet of Fire” alone.