This would have gone out at the height of my ten-year-old interest in "Dr. Who" but I can't say I recall it at all. It looks as if they have cannibalised the set from the infinitely better "Robots of Death" (1977) for this weak adventure for Tom Baker and Louise Jameson. The "TARDIS" inexplicably lands on the very cusp of known space just as the "Minyon" race is facing some sort of existential crisis. A ship under the command of "Jackson" (James Maxwell) is desperately searching for a previous expedition upon which their entire genetic history was placed in two gold cannisters. After a distinctly rocky start, these intrepid explorers find themselves on a plant occupied by the "Seers" who serve the "Oracle" - but might these peoples be the "Minyon" travellers they are all seeking? The one thing these series always steered clear of was visual effects. They knew they hadn't the budgets to do it well, so focussed more on solid stories and characters instead. This one rather bucked that trend and though I did quite like their shields armed with ray guns that we do actually see fire lasers, that means that much of the rest of this is set against a green-screen and time has not been kind on that front. As the title suggests, a lof of this is set underground - but instead of using the usual caves and quarries that Jon Pertwee knew so well, these are clearly studio imposed and at times they look ridiculous. The final quarter is rushed and on the whole this suggested to me a shortage of funds at the BBC and so this drama was created as part of an economy drive. Somehow it signals that Baker's time as the "Time Lord" hasn't long to run, and this is amongst the most forgettable of his enterprises.