Okay, the ultimate in "we have no budget but want to make something anyway".
Terrance Dicks gets given two sets, a Sontaran (looking decent this time), a Draconian and Sophie Aldred. He also gets given a gorilla mask and told to work that into it as well. Thirty minutes of talking later, the man in the gorilla mask declares the experiment over as the three others decided to get along with each other and not fight. And as it's Terrance Dicks, the polarity gets reversed to save the day. And that's about it really. Thirty minutes of aliens being nice to each other.
Yet it's surprisingly watchable. Everyone gives it their all and plays it deadly serious (even when faced with the monkey man) and only the very last word on screen lets it down (making it clear who they wanted Sophie to be playing but couldn't get the rights). It's not deep and meaningful but it's diverting enough and if you do have half an hour to spare, worth a look.