Just one small question. Why do you want to blow up the world?
Thus far in its four seasons, Doctor Who has had its share of evil villains bent on controlling the universe and dastardly foes driven by petty greed and egotism, but not until Geoffrey Orme’s “The Underwater Menace” (Story Production Code GG) do we get a truly mad scientist for the Doctor face off against. And oh, boy, is Zaroff mad.
In some ways, using a monomaniacal scientist determined to prove his genius by accomplishing that which no other scientist ever has—to wit, blowing up the planet—turns Zaroff (Joseph Fürst) into the kind of monster that the show’s original “no monsters” remit tried to avoid; first season shows in particular featured opponents who were driven by complex and internally consistent, though perhaps misguided, desires, like Tlotoxl and Autloc in “The Aztecs” or the eponymous Sensorites. Zaroff just wants to blow up the planet like some human Dalek, and as such, he provides no real challenge for the Doctor and his trio of companions, wasting the elaborate stage production of “The Underwater Menace” in the process.
With new companion Jamie aboard, the TARDIS shows up on volcanic specks of rock in the Mediterranean, the only above-water vestiges of the Lost Continent of Atlantis. Polly finds a medallion from the 1968 Mexico City Olympics near a cave mouth, to help place the story sometime in the late 1960s or early 1970s; it must have been dropped by a shipwreck survivor who was, like the Doctor and friends, captured by the Atlanteans, who use such people as sacrifices to their deity or as labor in their mines or sea farms.
Those sea farms, producing plankton and tended by slaves who have been implanted with plastic gills, cause the Doctor to dive into his Five Hundred Year Diary and come up with a name that saves them from becoming shark food as an offering to Amdo, the Atlantean god. He remembers that a Professor Zaroff, thought to have died in the 1950s, devoted his efforts to feeding the world through plankton, and by brandishing this name, he secures an audience with Zaroff, sparing his companions in the process. As he does so well, the Second Doctor plays to Zaroff’s ego in order to learn all he can, and it transpires that Zaroff has promised to raise Atlantis back above the sea. He just intends to lower the oceans by dumping them into the Earth’s molten core rather than lifting Atlantis itself, though, with the slight side effect of causing the planet to explode. When the Doctor notes this outcome, Zaroff readily acknowledges this result as a feature, rather than a fault, of his plan. Where are the rational Daleks when you need them?