Alright, just finished TotP Part3. Overall, it did an alright job developing the innkeeper and explaining the situation, though (as usual) I unearthed a multitude of minor problems.

I note there's a few places where you explain problems I noted in previous chapters, and for the most part they all read smoothly. This one, however, just feels out of place, like you only put it in to cover a continuity error. I think in part it has to do with the use of parenthesis. Imagine a character falling off a very high cliff and surviving, and saying "It's a good thing some people are extremely bouncy (like me)." Using parenthesis like that is, if anything, specifically for humorously defending a continuity error.
Moreso, though, it's important to consider the definition of "ranger". Even if you draw from Dungeons and Dragons influence, you have to remember that a character's "class" isn't just something they picked off a list. Rangers in fantasy are usually people who defend a natural area or nature as a whole via their tracking and hunting skills, so working as a guard in a city is likely outside their "comfort zone" (unless they are guarding the vicinity around the city). Furthermore, the ability to talk to animals is presumably not "because they are rangers", but a skill that they picked up from being outdoors so long.
Also, it is pertinent to differentiate between "talk to animals" and "understand animals", and having animals understand you is another thing entirely. Anyone can talk to animals and, though this is never clarified, I presume Slipstream can understand English.
So really, it seems unrealistic that one of the guards would happen to be a ranger, and thus perfectly understand every animal. More likely, one of them would happen to understand a sufficient amount of Horseish to get the general idea of what Slipstream was saying. There are definitely different "levels" to understanding any language.

On an entirely different note, "guffawed" doesn't sound right. It means to laugh, and someone waking up doesn't strike me as particularly funny. Also, typo! You said "the room was quite", not "quiet".

So, a knight in black armor. "That sounds just like some other evil person" is a somewhat hasty conclusion. I mean, it is a typical rule that the bad cowboys wear black hats, so to speak, but characters usually don't openly acknowledge this. The innkeeper also mentions that the knight was a ranger because he could talk to a horse, which, as I mentioned before, doesn't really work. Also, can someone be a knight and ranger at once? I'm not sure.

Anyway, there's something strange about the line "I took some spells and left". Presumably, what Keiy took was either spell scrolls, or he learned some spells.

Lastly, I think this line would work better as "they want our world back":"Planet" is a word for large rocks floating through space. The very etymology of the word can be traced back to the Greek word for "wanderer", as planets were initially viewed as things that wandered across the night sky. Thus, a "planet" is something comparatively small, as it is held in relation to space.
"World", on the other hand, is a more "vast" word. People think of a world as a big thing, because it's being compared to smaller things on it. Most importantly, though, is to consider that this is presumably a pre-space travel culture you are writing about, and there is likely to still be differentiation between planets and the world.