The Underwater Menace is one of the few really off-beat stories of the Troughton era, with “ballet-dancing fish people” a slightly Web Planet-type adversary, suffused with a similar bizarreness. Coming after Dalek scheming and purely historical hijinks, “Fish People in Atlantis” are the first original antagonists of the Troughton era: this would normally be the point at which we are bedding in, settling down with a new template for the new era, making some effort to be ‘the new normal’. But as we know it’s yet another false start; the true Troughton norm will not be established until the following story where it finally hits upon the “base-under-siege” template which will work such wonders for the ratings over the coming years.
Personally, I go for weird and wacky over base-under-siege. The Underwater Menace is not the most polished production in the world; despite featuring a veteran screenwriter with Ivanhoe to his name (Geoffrey Orme), a solid director (Julia Smith), and a renowned actor (Joseph Furst), the whole thing was made for about 50p and as a last-minute replacement for The Imps by William Emms, and each episode was only filmed the week before it was on TV (even Troughton flubs a few lines here, common for his predecessor but pretty rare for him). Orme is the second veteran writer for Season 4 after Elwyn Jones, a sign perhaps that Lloyd and Davis were looking to hire the big TV names of the day. And yet what Orme turns out probably wasn’t quite the crowd-pleaser they were expecting, but rather a surreal romp under the sea, as a completely mad scientist tries to raise Atlantis above the waves. Orme borrows from Verne, Wells and classic comics (20,000 Leagues under the Sea, Flash Gordon, Journey to the Centre of the Earth and The Island of Dr Moreau) but this is, even looked at charitably, a 50s B-movie.
You can read my take on the third episode here.