While I wouldn’t go as far as to call this the worst Doctor Who story ever, this is the silliest. The premise is perfectly sound, with an alien ambassador looking to trade metal for nourishing chlorophyll with a planet rich in vegetation, who gets mistaken for a monstrous invader and forced to live in an underground mine for years. The ruler, Lady Adrasta, wants a controlling monopoly on the metal market, which has led to a nation ruled by fear, and the creature in the pit used as punishment.
There comes a point where light-hearted humour becomes daft silliness, and I think this story is that tipping point. For example, having been thrown into the pit, the Doctor, clinging on for dear life, finds the time to reach into his pockets and pull out a book on climbing Everest, discovers it’s written in Tibetan, then pulls out another book for learning Tibetan. The whole sequence is played for laughs but it feels very silly. Then there’s the creature’s tentacle, sliding around the mines. I don’t know if this was played for laughs as well or if it’s just unintentionally hilarious, but the thing looks… unfortunately phallic. I nearly burst out laughing when it appeared. I couldn’t take it seriously.
Then there’s the wolfweeds, living balls of plant-stuff that roll around at the beat of a whip (huh?), K-9 being used as a talking raygun (lame), and a sequence where the creature encases a neutron star with metal (far-fetched). To top it off, it’s not even a particularly interesting story; I was bored by it.