I think I’m starting to see why people dug the Fourth Doctor so much. Granted, someone knocks him out again in this episode. He really needs his predecessor’s martial arts skills sometimes.
Those skills would have come in handy when the mostly-mutated Noah had him cornered. Fortunately, Sarah Jane and Vira show up to shoot the thing. That doesn’t kill Noah, but it does allow the Doctor to escape. He and the women manage to sneak around until they get to another control room where Harry and Rogin are waiting. By now, the Wirrn are hatching and swarming the ark. The one that was Noah is offering to let them leave in the escape rocket so long as they leave all the other still sleeping crewmembers behind. Will that work? Harry suggests using the TARDIS, but that isn’t a solution this time. If only they had a power source to run electricity through the entire ark…
Wait, the escape rocket has that! And they have a long wire! If the Doctor can rig things right in the cryo-chamber (and he can), then they just need to run the wire to him.
Of course, with Wirrn everywhere, how would they do that without being seen?
They could go through the ventilation shafts. You know, those thin, twisting shafts.
Sarah Jane then points out she is thin enough to fit through the vents. And so, with Harry, Rogin, and Vira guiding her from the escape rocket and the Doctor waiting on the other side, in she goes.
She does get stuck close to the Doctor’s end, but he just makes a lot of remarks about female inferiority. That makes her mad enough to push through. And then he’s nice again, so it was all a ruse.
So, the electricity mostly works. Wirrn attacks the escape rocket, but there’s nothing a blast of the engines won’t fix. What do the Wirrn want anyway?
Well, it seems they reproduce using other living things. And if they do it to the humans, they’ll gain humanity’s technical knowledge. That plan sounds bad for a lot of people. Plus, since they don’t need air to breathe, they can also climb over the hull to get to the everyone that has now clustered around the escape rocket. Only thing left to do is let that rocket blast off and kill the Wirrn. Everyone makes a run for it save Rogin and the Doctor. Someone needs to keep the rocket ready to fly off. Rogin just knocks the Doctor out and does it himself.
Funny thing, Noah could have stopped the rocket. He was still human enough to choose not to. Humanity is saved. The Doctor tosses out a jellybaby, and he and his companions are free to move on.
Take that, giant bugs!