Well, the Doctor has his work cut out for him if he doesn’t want one of his companions to be a permanent host for an evil snake entity.
Well, first, he’ll need to escape the palace since Lon wants the Doctor, Nyssa, and the young archaeologist executed. Seeing as how Lon is also possessed by the spirit of the Mara and he’s wearing those gloves to hide that fact, there isn’t much the Doctor can do. You know, until Lon’s mother shows up to point out how that sort of thing isn’t done. Oh sure, there can be a trial and all, but these space Ren Faire types don’t go all out on execution.
But since the Doctor can speak, he asks to see the Great Crystal, and since the older archaeologist has it, he opts to maybe take it out. Since that’s a distraction, the Doctor and his two friends can make a run for it.
Now, we’ve seen some old man meditating out in the desert off and on in every episode thus far, so he must be up to something, right? Sure. After the Doctor gets some lessons on local customs, the young archaeologist takes the Doctor and Nyssa out there, and after a minute, the old man appears. He and the Doctor then do the Snake Dance ritual, fulfilling the serial title’s requirements. That ritual has both men get a bite on the wrist from a small snake, after which they can communicate telepathically. The Doctor is advised to find his “still point” to defeat that lousy Mara.
Since the Doctor does have a lesser crystal, that may work. He and his friends head back to the city to save Tegan from the direct control of the Mara and everyone else from whatever else it is the Mara does. He’s more or less too late as Lon shatters a false Great Crystal before putting the real one into a wall, conjuring the snake and causing it to grow in what is, for this show, not a completely terrible special effect. You know, until it appears as if Tegan’s face is in its mouth.
Maybe it’s the bad effect or maybe it’s the Mara’s awesome psychic power, but everyone in the crowd suddenly loses it, falling to their knees and crying and wailing and probably gnashing their teeth–except the Doctor. Like opening the Arc of the Covenant, he knew not to look. Granted, no one is listening to him urging them all to be calm because the Mara feeds off fear, not even Nyssa, but Nyssa hasn’t really done anything right for this whole serial, so why start now?
Since the Doctor focuses inward to his still point, he’s able to resist the Mara long enough, with help from the old man, to pull the Great Crystal from the wall and destroy the Mara once and for all.
Or so he tells Tegan since she’s fine now. You know, aside from the trauma.
Well, that’s it for this kooky planet. Next serial features the return of an old Doctor Who ally as well the first appearance of a new companion for the Doctor.