There's a lot in this episode that I enjoy. This season of Discovery really did go into so many of the kinds of stories I most want to see, and that makes me really excited, even on a re-watch.
Culber is in the hospital having tests run on him after his body was reformed. The doctor confirms that, while his brain scans are normal, his entire body has been reassembled from his DNA. This is clearly distressing to him, and he doesn't feel like himself. It's an understandable reaction. It has to be jarring to suddenly be in a new body. He's even missing his scar that inspired him to be a doctor. That probably felt like a big identifier for him, so it would be a big shock for it to be gone.
This storyline raises a lot of interesting questions about what makes a person and how much is it tied to what makes you a person. If Culber's entire body has been reformed, then that means his brain has too. Even if his brain scans are normal for him, there's still a question there of if he is actually himself or is he more along the lines of a clone of his former self who is now dead.
What's strange to me is that no one else notices just how distressed he is by all of this. It's clearly written on his face in every scene he's in, yet people keep going on as if everything is perfect. On one hand, I understand this could be because they're so relieved to have him back that they can't imagine why he would be upset. That's especially true of Stamets, who I didn't find it surprising from, but it's just strange that no one clues in to just how upset he is. It's also strange to me that, despite their advanced medicine, no one thinks that going through something like having your body reformed would warrant a psychological evaluation immediately. (Yes, they performed brain scans, and we don't know everything those covered, but clearly, that wasn't enough.)
We also get a bit of information about Saru right off the bat in the episode: His fear response is being suppressed. Not long after, there's another signal from the Red Angel that just so happens to have come from Saru's homeworld Kaminar. The rest of the episode is heavily focused on Kaminar and the truth about the Kelpiens and Ba'ul.
This is one of my favorite subplots in this season. I find the history of Kaminar fascinating enough to warrant a whole season on it. The Ba'ul were almost wiped out yet managed to develop technology to both save themselves and oppress the Kelpiens. That story alone could be a whole show. The Ba'ul also appear to have lived in the water yet now live on space ships (or maybe some still live in oceans on Kaminar and we didn't get to see it) that has huge story potential too. There's so much there!
The way the Ba'ul are characterized is also interesting. Both their voice and bodies are clearly meant to be terrifying despite what we learn about them in this episode. They're characterized more as predators than prey even though their bodies appear rather frail from what we see of them. (Admittedly, the Kelpiens don't look like a typical portrayal of a "predator" either.)
Neither Kelpiens or Ba'ul fit neatly into "predator" or "prey" considering they've each been both at different times in history, but it was still an interesting choice to portray the Ba'ul the way they did visually.
Once the Discovery and Saru's sister, Siranna, learn the truth. They're committed to telling the Kelpiens the truth and creating a "new balance." This desire makes sense. Obviously, as Kelpiens, Saru and Siranna would want their people to know the truth, and I'm happy that they want to achieve peace instead of destroying the Ba'ul.
However, everyone seems quite convinced that, if the Kelpiens learn the truth, they will inevitably come to live in peace with the Ba'ul instead of the cycle of one destroying the other continuing. It's optimism to a degree that feels foolish. Personally, I'm sure it could be possible, especially in a fictional TV show, but it would be a huge struggle that would undoubtedly involve violence to a certain extent (which is kind of acknowledged), and it feels like the show just leans on "everything will work out great in the end" a little too much there.
When the Ba'ul try to destroy every Kelpien village, the Red Angel intervenes and saves the Kelpiens. Saru sees the Red Angel and reports back that it's "humanoid" (which is an interesting word choice considering what I've said before about it being a weird "coincidence" that so many sentient aliens look like humans) and has advanced technology. Time travel is mentioned for what I think is the first time this season. But the Red Angel's identity is really as much of a mystery as it was before.
The episode ends with Michael declaring that she needs to return to Vulcan, so we know exactly where we're going in the next episode.