Hidden Agendas is one of those short corebook-overflow supplements that White Wolf liked to do. It's filled with odds and ends, and is mostly pretty interesting, but it doesn't go into depth on any one subject and the material is not connected by a theme.
The biggest surprise for me was learning that the Trinity universe has space pirates. I guess this is something that maybe I should have inferred, based on the fact that spaceship stats were printed in both the Core and the Technology Manual, but I don't know what to tell you. I guess I had the vague feeling that they were supposed to be rare. You can't have pirates if the very fact that you're in a spaceship automatically narrows down the pool of suspects to, like, eight guys.
So I went back and checked the earlier books. I'm vindicated by the confirmation that none of the other entries directly mentioned pirates. However, I'm also embarrassed to learn that the one time we get hard numbers for a spaceship's production run (for the Offworld Enterprises Ltd Pathfinder freighter) the figure is 100 ships a year, with probable demand easily being twice that much.
The funny thing is that I have no excuse for this. I remember reading these spaceship descriptions quite clearly. I think what happened is that I internalized the idea that space travel = interstellar travel, and there is a legitimate bottleneck when it comes to FTL. Only the teleporters and the new jump ships can make it, and there is explicitly only one jump ship, now that the Upeo Wa Macho have disappeared. I guess I just forgot that there could still be a lot of traffic between areas of our own solar system.
This book mainly discusses their ambush and combat tactics, but unfortunately doesn't get too deep into their culture or history. There's enough material to inspire an adventure (I like the idea of rescuing someone who is being held hostage aboard one of their vessels), but not quite enough for a campaign.
There's also a tantalizing bit of metaplot here in the section about fringe religion. There a new cult that worships the hidden progenitor aliens who empowered the Psi Orders, and though the text implies that they're mostly guessing about that, the group's name is the "Doyo." Do they genuinely have contact with the Doyen or is the name based off of something else? Intriguing.
That section also answers another niche question that I would never have thought to ask, but which I remember from a Baha'i's commentary on the religion's use in Trinity. The reason the Baha'i headquarters was relocated to the moon is precisely because they were kicked out of Mount Carmel by Temple Judaism.
It's a plot point that makes me vaguely uncomfortable, just because there's no clear indication of Temple Judaism's context within the greater Jewish faith. Having a rogue sectarian faction close the borders of Israel is maybe the sort of story you could tell in a sci-fi universe, but only if you center it on the Jewish diaspora and the displaced local population. Without having Orthodox and Reform Jews sitting on the sidelines disapproving, Temple Judaism feels kind of antisemitic. Unintentionally, I'm sure, but it's definitely something they should have spent more care on.
What else? Let's see . . .
Antarctica is rapidly become a capitalist hell-hole, but the process is slowed because the continent is mysteriously cooling. I know global warming wasn't as big an issue in 1998, but that's a weird plot hook.
Also, the Antarcticans call themselves "Borealites," which is a neat name, but wrong for the hemisphere.
Some Chitra Bhanu may have survived. Further details will have to wait until they write some.
There may be an AI in the Trinity universe, but it's not directly confirmed, and the book it would have been in (The Ministry splatbook) was never published.
Finally, swinging back to pirates, they occasionally use fusion warheads to attack ships, implying that such things are commercially available. I don't even want to think of the setting implications.
Overall, Hidden Agendas was a fun book and a quick read, but nothing that I was terribly missing from my Trinity collection (aside from the obvious bit about the ubiquity of space travel, that is).
Ukss Contribution: There's a brief, but desultory section about an avant garde architect that had some neat sci-fi buildings. My favorite was The Summit Center. A big skyscraper that was mounted on a rail that circled a Martian crater. It made one revolution per day for no apparent reason. Every great science fiction or fantasy setting has to have something so pointlessly impractical.