'Planet of Evil' has fallen on hard times. Back when fans' only knowledge of old Doctor Who stories were hazy memories story guides like that in Doctor Who: A Celebration, 'Planet of Evil' was a terrifying story that drew on Dr Jekyll and Mr Hyde to great effect and was even compared to Alien, as a monster picked up on an alien planet slaughtered the crew of a spaceship. With the video release however, opinions became rather more divided, and 'Planet of Evil' was found by many to disappoint. But 'Planet of Evil' doesn't really deserve its poor reputation. Whilst it is overshadowed by the stories on either side of it, it still has much to offer.
Firstly, the jungle set, one of the story's most famous aspects, is pretty good. It looks suitably different from any jungle on Earth, and its rubbery vegetation gives it a very alien feel, which is enhanced greatly by the wise decision to shoot many of the jungle scenes on film. Indeed, Zeta Minor is one of the most unearthly alien planets seen in the series, with its weird foliage, non-reflective black pool and the Anti-Matter monster. The monster too is far more alien than many seen in the series, due to its appearance as a red outline (an obvious, but effective homage to Forbidden Planet), and the fact that unlike many intelligent aliens in Doctor Who it doesn't speak English, its only communication with the Doctor achieved through a surreal scene in a black void.
Set amidst this alien landscape, Episode One gets off to a promising start. Sorensen sets the scene with his terse assertion that the planet is alive, and the deaths of the two Morestrans are dramatic and disturbing, as they vanish screaming in agony, only to reappear as quite convincing shriveled corpses. The sense of danger established in these early scenes is maintained throughout, with the Anti-Matter Monster and the Anti-Men well nigh unstoppable; the tension in Episode Four as the marauding advance through the ship and agonized screams are heard over the communications system, whilst the ship plummets back towards Zeta Minor is palpable. However, flaws start to appear in Episode One as the Doctor and Sarah are imprisoned in a room from which they can easily escape; admittedly the script addresses this, and it gives Sarah something to do since it is she who realises that with the failing power the magnetic window locks will have weakened, but it feels very contrived.
I'm in two minds about the Morestran probe ship sets. They are very sparse, and this contrasts sharply with the jungle on Zeta Minor, and this makes a certain amount of sense since it further enhances the planet's alien feel and also military vehicles are not renowned for their décor. On the other hand, these sets are so stark and featureless that they are actually boring to look at, and ironically the comparatively moody lighting in the corridors makes them marginally more interesting than the command area. The Morestran costumes are also pretty awful, which doesn't help the story's visual appeal during the latter two episodes.
In addition to these minor flaws, there are two aspects of 'Planet of Evil' that I originally considered to be weaknesses, but as the story progressed I found that, bizarrely, they actually added to the story. The first is the anti-matter plot line. As Kate Orman has pointed out, anti-matter does not cause people to turn into ape-men, it simply causes huge explosions in collision with matter. Initially, this makes this plot seem like pure technobabble, but then in Episode Two, during a conversation between the Doctor and Sarah, it is pointed out that matter and anti-matter in collision causes a massive release of energy (as seen in 'The Three Doctors'). Suddenly, by addressing this inconsistency, the script makes the anti-matter plotline seem less like technobabble and more like intentional fantasy, and in doing so adds further to otherworldly nature of Zeta Minor, subtly reminding us that this unique planet is a gateway between universes, neither entirely in this universe nor the universe of anti-matter. This also ties in with the Doctor's implication that if the Morestran ship manages to get too far from Zeta Minor with anti-matter on board, there will be a cataclysmic explosion that will threaten the entire universe, suggesting that Zeta Minor exists in a state contrary to the laws of physics.
The second aspect is Salamaar. In my opinion, there is no evidence in Doctor Who that Prentis Hancock can act; he was wooden in 'Planet of the Daleks' and he's wooden here, although it doesn't help that he's playing very similar characters in both stories. Nevertheless, Salamaar the character is rather interesting. He's ludicrously unstable and clearly unfit for command, making reckless decisions and twice intending to execute the Doctor and Sarah simply because it will make his life easier if they are responsible for killing the Morestrans on Zeta Minor. When he eventually accepts the truth, he adopts a death and glory attitude, launching a suicidal and misguided attack on Sorenson that further endangers the surviving crew. Initially, I found it absurd that such an unstable character could become commander of a military expedition, but as the story progressed this too made me think; there are hints that Sorenson's influence back on Morestra will get him whatever he wants, and once these hints of corruption are sown it raises the obvious possibility that Morestra is so corrupt that Salamaar himself reached a high ranking position because of friends in high places. This is further supported by the fact that the much more competent but disruptive Vishinski holds a lower position, raising the possibility that his outspoken nature has harmed his career.
The acting in 'Planet of Evil' is variable. Tom Baker and Elizabeth Sladen by now play their roles with ease, and the Doctor gets to be suitably impressive here, claiming that he is not without influence and proving able to communicate with the Anti-Matter Monster. Sladen is convincingly frightened at appropriate moments, especially the cliffhanger to Episode Three and during the final attack of the Anti-Men in Episode Four. Frederick Jaeger is superb as Sorensen, playing the tortured scientist with great emotion. Sorensen's initial obsession with his work is so all consuming that he blames the Doctor and Sarah for the deaths of his colleagues and strenuously denies both the Doctor's claims about Zeta Minor and also the transformation that he is undergoing. But Jaeger suggests that Sorenson is also troubled by his conscience, and his quiet confession to the Doctor in Episode four that "My hypothesis was false" has rather a noble ring to it. In story terms, this admission seems to bring him redemption, and the Anti-Matter Monster unexpectedly cures him at the end of the story. Vishinski is also well acted by Ewan Solon, but the other Morestrans are utterly forgettable, with one or two (Ponti being a prime example) being quite bad.
In summary, 'Planet of Evil' is flawed but effective and certainly doesn't deserve its recent poor reputation. In a weaker season it might stand out more, but as it stands it is overshadowed by both 'Terror of the Zygons' and the story that follows