That, Doctor, is a kilt.
If ever a story could explain the demise of Doctor Who‘s UNIT era, Robert Banks Stewart’s “Terror of the Zygons” (Story Production Code 4F) fits the bill. This, the penultimate UNIT story, shows just how out of sync the militarism and regimentation of the Brigadier’s bunch has fallen from the frenetic energy and mordant sarcasm of the Fourth Doctor. Where UNIT’s deployment of mortars and bazookas and lots of lads shooting rifles not quite straight added to the visual excitement of the Second and Third Doctor’s adventures, here they just get in the way of the Fourth Doctor’s investigation of the Loch Ness Monster.
Indeed, it’s odd that most Third Doctor UNIT stories did not suffer greatly from the presence of Lethbridge-Stewart, Benton, and Yates, given that regeneration’s incredible disdain for military solutions; the Fourth Doctor, by contrast, shows no great compunction about blowing the beasties up and would seem a better fit in theory. The friction comes much more from stylistic approaches, as well as a tendency towards four episode stories in Tom Baker’s era. In “Terror of the Zygons,” Stewart’s plot spends scant enough time on the shapeshifting Zygons who have hidden in Loch Ness for hundreds of years; the inevitable padding that comes with the Brig telling Benton to call someone on the radio which then fades to location shots of UNIT troops milling about a forest just eats up valuable screen time. One can almost hear the audience groaning for the action to shift back to the Doctor. And, of course, nothing UNIT does actually changes the direction of the plot in the least.
Right from the start, the Doctor shows his irascibility at the Brigadier for summoning him back to Earth for so trifling a matter as the destruction of a few oil platforms off the Scottish coast. Only the siren song of a mystery can get this Doctor interested, and finding tooth prints of an enormous beast in the rig wreckage does the trick. Stewart does a nice job of not mentioning Loch Ness until deep into the second episode, allowing viewers to piece together the appearance of a long-necked prehistoric creature with the Scottish moorland setting before finally springing the connection.
Doctor Who is often associated with this trick of using an unexplained real-world phenomenon as a plot device, elucidating the incident in the course of advancing the narrative—aliens are almost always responsible—but in truth, this technique dropped off after the first few seasons, the last instance coming in Season Five’s “The Abominable Snowmen.” In this case, the mystery might have been better left unexplained, for the Zygons use the Loch Ness monster as…a milk cow.