This is season eight, which is just one four part story. Clearly they knew they were going out and decided on one big band. This is War of the Empires.
The Thargons and the Sausons are the empires having a war, and they are battling near a closed world, also known as Earth. The TPs are trying to stop them, and when the earth becomes threatened, they step up their efforts. However, we need a nation on earth that is friendly, but otherwise an arrogant brutal warmongering... and that's not British, so say hello again to the Americans! They join forces with the Sausons(*) for a bit, but the TPs convince them to help eventually to see them all off. While the TP try to get the Galactic Federation involved, but instead end up evicted, so it's up to them to deal with everything.
(*)I think. I quickly lost track who was who... btw, this is one lot of them (the others are just people in military outfits with gold paint everywhere):
But, hey, speaking of the Galactic Federation, we have this lot:
Galactic Council, eat your heart out! And we have even less information about who any of this lot are except Timus and the chairbeing.
Anyway, this story is all go, and actually the TP are right in the thick of it from the word go and remain relevant all the way through. They drive a lot of the plot, and it's up to them that earth survives. This is great, this feels like a decent story and... okay, there are still too many TPers to get properly served, and we could easily lose one without noticing, but it's still good.
This is a good story to go out on, and aside from those stupid aliens, I would recommend people checking this out.