Danger Down Below features the Doctor, Tegan and Nyssa. At the beginning of the story it is mentioned that Nyssa is staying in the Tardis because there is no requirement for more than one Companion in this story.
The Doctor has come to the planet Aronassus 49 to help his "old and dear friend, High Minister Threll of the Prime City Triumvirate." The mannys of Aronassus 49 are starving because all their noms are going missing, which sets up a mystery and gets the plot going very quickly
I like how the positions of the Doctor and Tegan in this picture are very similar, but not precisely the same, as in the first picture.
The Doctor and Tegan are observed, and then captured, by some guards who think they are the ones who have been stealing their noms. The dialogue manages to capture Davo's portrayal of the Doctor:
Tegan got up from the bed. "What happened?"
The Doctor turned to face her. "Neuro-paralysis dart. Not exactly the welcome I expected."
The Doctor's friend Threll quickly releases them, so the paragraph of them being captures reads like the sort of pointless captured-and-escape padding of the TV show.
The guards are still suspicious though, and this becomes a plot point later on.
The Doctor has chubby cheeks in this picture. Maybe he has been stealing all the mannys' noms!
Threll tells the Doctor that some of his mannys were electriced. The Doctor shows Threll a black ball that he found. It is time for some exposition:
It was soft to touch, yielding under finger pressure. "I found that on the surface," the Doctor said.
Threll shuddered at the feel of the thing. "It feels alive!"
"It is-it is one of the killers of your men."
Threll stared at the Doctor, then back at the thing. "This?" he said incredulously.
"Not on its own. By itself it has only limited power. By the hundred they could devastate a complete city."
Tegan moved over to look at the thing, overcoming her revulsion. It was pulsing now, like a tiny heart. "What is it?"
"Another galaxy's equivalent of our own bodily defence mechanism, like a white corpuscle. The only difference being that these live outside the body they protect, stopping any dangers approaching their host."
Threll was taken aback. "Like my men," he said grimly.
The Doctor nodded. "Whatever they are protecting down in the production plants is not a threat to you -you are a threat to it."
"A being from another galaxy! I never dreamed..." Threll trailed off.
The Doctor wants to resolve things peacefully, but then Chief Guard Sholl comes to arrest the Doctor, Tegan and Threll. It is clearly time for a cliffhanger-style moment:
"The sentence for these charges," he continued, "is immediate death."
"No, you fool!"
The black ball saves them by flying into and electricing Sholl and his guards.
Threll takes the Doctor and Tegan to look for the black ball's host alien, and they have to stay ahead of the rampaging mob of hungry mannys that Sholl had following him. The black ball electrics anyone who gets in their way, and they make their way to the place where the mannys keep their "food processing machinery".
Tension is quite skilfully built over the course of a few sentences before the reveal of the creature. Or we could look at the picture on the same page...
The creature occupied most of the large food distribution chamber. It was amoeba-like, almost like a gigantic human cell in appearance, and its flesh undulated and rolled like slow-motion waves, sending green tendrils snaking across the floor; tendrils that enveloped cases of Prime City food supplies and drew them back to the main body, which absorbed them.
The Doctor recognises the creature as a Migrator, from the Andromeda galaxy. He thinks it is on this planet by accident, and decides to take it away in the Tardis. Leaving Threll and Tegan behind (where they are protected from the mob of mannys by "a veritable army of defence balls"), the Doctor goes back to the Tardis and materialises it in the room with the Migrator.
When he was ready, the Doctor called Tegan and Threll into the time and space vessel, where they met a bewildered Nyssa, crushed up against a wall by a somewhat cramped Migrator, Threll could see that the Migrator's bulk had oozed through other doors and was probably enveloping a goodly portion of the maze-like Tardis corridors.
The Doctor ejects the Migrator into deep space, where it is apparently going to be fine. The story ends with the Doctor offering to take Threll back to his planet a week in the future, to give the mob of mannys time to calm down.
"I think by that time," Tegan observed, "your people should be glad to see you." She smiled. "I'm looking forward to your reinstatement as High Minister."
"And I," said the Doctor, "am looking forward to a really good meal."
Danger Down Below isn't a great story - it's a bit bland, a bit predictable, and a bit light on dramatic tension. The best that can be said for it is that it captures the feel of the TV series of that era well.