'Planet of Fire' is decidedly odd. Writer Peter Grimwade is given numerous ingredients to incorporate into his scripts, and as in 'Mawdryn Undead' he does this rather well; whereas in that story he had to cope with the Brigadier, the Black Guardian and a new companion, here he has to write out Turlough, tie up the dangling plot thread that it Kamelion, introduce new companion Peri, and include the Master. Given these criteria, it is impressive that he manages to create a coherent plot at all; that he manages to give Turlough a decent back story and provide the Master with his best story in some time is a minor miracle.
Turlough's final story sees his past revealed, as we discover that he is a political prisoner from Trion, exiled to Earth following a civil war. The story serves him well, and Mark Strickson puts in a fine last performance as Turlough comes to terms with his past. Initially, he's shifty and deceitful, as the TARDIS intercepts a signal from a Trion beacon; he sabotages the TARDIS, misleads the Doctor, and is more than willing to "finish" Kamelion to prevent his people from finding him. As the story progresses though, his more heroic side emerges, as he realises that Malkon is his brother and places the safety of the people of Sarn above his own continued freedom. Strickson conveys throughout the fact that Turlough is wrestling with his conscience, and it works very well; his eventually discovery that his exile has been rescinded nicely finishes off his story, as he returns home whilst, as the Doctor puts it, he's a "bit of a hero". And he is indeed, a bit of hero; after the TARDIS arrives on Sarn, he gradually accepts responsibility for the safety of its people, whose fiery planet was tamed by the Trions so that they could use it as a prison colony, and it is Turlough's understanding of the remaining Trion technology that allows him to save Malkon's life, and save the people of the settlement. His final scene, as he parts company with the Doctor, is a great moment; the quiet friendship and mutual respect between them is perfectly summed up by Turlough's reluctance to leave the Doctor, and the Doctor's quiet declaration that he'll miss him. And given that he describes Brendan School as "the worst place in the universe" it's nice to see him finally change out of that bloody uniform!
The other departing TARDIS crewmember is of course Kamelion. Having been introduced as plot contrivance in 'The King's Demons', behind the scenes difficulties with the prop meant that Kamelion did nothing except lurk unseen in the TARDIS until 'Planet of Fire'. Craig Hinton and Christopher Bulis may have made use of him since (in 'The Crystal Bucephalus' and 'Imperial Moon' respectively), but he did nothing whatsoever on screen during that time. Following on from his introduction, Kamelion is once more used as a tool of the Master, who reestablishes contact with his puppet and uses him to lure the TARDIS to Sarn. As such, Kamelion is once more used as little more than an instrument by the Doctor's old enemy, and spends most of the time played by Anthony Ainley or Dallas Adams. Kamelion gets a rough time throughout the story; it was established in 'The King's Demons' that he can't resist the Master, but circumstances on Sarn mean that he doesn't even get sympathy from the Doctor, who refers to him as a puppet and generally belittles him in an attempt to overthrow the Master's control. Eventually, the Doctor is forced to induce the equivalent of a heart attack in Kamelion in order to stop his old enemy. But to his credit, Grimwade does at least give Kamelion some characterisation of his own; the scene in Episode Two in which he desperately shakes off the Master's influence just long enough to allow Peri to escape and try to reach the Doctor shows that he is not a willing servant of the Master. His final scene is also rather tragic, as he pitifully apologizes to the Doctor and begs to be destroyed.
With Turlough departing and Kamelion destroyed, the Doctor is provided with a new companion in the form of Peri. The lingering shot of Nicola Bryant in a bikini in Episode One leaves little doubt as to what John Nathan-Turner was looking for in the role, obviously hoping to appeal to the heterosexual male audience, but fortunately the character comes across as more than just a pair of assets. Her decision to swim ashore when her stepfather Howard leaves her trapped on the boat in Episode One is foolhardy but brave, but where she really shines is in her scenes with the Master (or rather, Kamelion as the Master), to whom she causes considerable inconvenience. Her response to the Master's "I am the Master!" is, rather amusingly, "So what? I'm Perpugilliam Brown and I can shot just as loud as you can!" and later on she interferes with his attempts to harness the numismaton gas of Sarn both by interfering with his control of Kamelion and by attempting to swat him with her shoe. The character also works well with Peter Davison's Doctor, and her decision to travel voluntarily with him at the end promises a keen and enthusiastic traveler on board the TARDIS. Which doesn't last of course, but that's another story And Bryant's accent, famously convincing enough to fool John Nathan-Turner, is pretty good.
The other recurring character who plays a role in 'Planet of Fire' is of course the Master. His reduced circumstances mean that here is motivation is once more survival rather than a sudden desire to tinker with the boring bits of Earth history, and it is very welcome. Without the need for ludicrous survival, his appearance (via Kamelion) at the end of Episode One, is for once very effective, since he isn't revealed to have been posing as somebody else for no apparent reason. I addition, Anthony Ainley reigns in his performance to considerable effect; bereft of constant gloating and chuckling, he's far more sinister and intimidating than he is in his usual pantomime mode. He looks utterly mad when he says to Peri "allow me to introduce the tissue compression eliminator", for once seeming like a real lunatic rather than some moustache twirling stereotype. Best of all, the relationship between the Doctor and the Master here is handled far better than usual; the Doctor's tolerance for the Master is at an all time low, as demonstrated when he tells Turlough that if he is withholding anything that will aid the Master then their friendship is at an end. Davison's performance reflects this, as he puts in a far more testy performance than usual once he discovers the Master's involvement, and as noted he takes out his dislike for the Master on poor old Kamelion. Grimwade deserves a medal for the final confrontation between the two Time Lords, as the Doctor stands and watches his old enemy seemingly burnt to a crisp without lifting a finger to help him even when he starts begging. It is exactly how the Doctor should react after the carnage unleashed during 'Logopolis' and works far better than his concern for his enemy in 'The King's Demons'.
As for the rest of the story and characters, they are all window dressing. The background to the settlement on Sarn is adequate, if vaguely reminiscent of 'The Face of Evil', but the actual characters are largely forgettable. Malkon is only worthy of note because he's Turlough's brother. Timanov is an utter cliché, a stock religious fundamentalist who is more than happy to burn heretics; however, near-legendary Peter Wyngarde brings a certain dignity to the role, and Timanov's decision to die with his settlement seems strangely noble rather than futile. Dallas Adams switches from jovial but parental America scientist Professor Howard Foster to slightly creepy silver skinned android quite well and it's so unusually to see an actual American inDoctor Who that it deserves mentioning.
The production is competent, if unmemorable. The Lanzarote location work looks nice, although it only really benefits episode one; Sarn quite frankly could have been filmed in a gravel pit in Surrey. There are some good sets, especially the control room in the volcano, although the Great Hall of Fire and secondary control centre for the cave look very artificial. Mind you, director Fiona Cumming performs minor wonders; a miniature Master is a potential recipe for CSO flavoured disaster, but she makes it work very well in Episode Four. And as usual, Peter Howell provides a very good incidental score. Overall, the unusual nature of 'Planet of Fire' means that it could never be a classic, but is a reasonably successful story, albeit one that feels more like an attempt by the production team to tidy up the series before Peter Davison's impending departure than a story in its own right.