The Macra appear but it all forgotten about as the Controller tells the Pilot to forget what he saw on the screen.
Jamie and Polly are sent down the pit and look for gas. No one has a clue what use this gas has but it is lethal.
The Doctor might have a clue. He has figured out the formula much to the Pilot's shock and surprise.
As for Jamie, he goes snooping and confirms the Doctor's theory. It is there to keep something alive.
That something is the Macra and Jamie somes face to face with them.
Once again you can see the creative licence used in the animation. When the Doctor writes the formula, it is show from behind as the Doctor writes on a perspex screen. This mirrors a similar shot from The Day of the Doctor.
The episode feels stretched, even bitty. It really is holding fort for the concluding episode. At least Ben might be coming around to his normal self.