u/Automatic_Web_2630

The answer, thanks to AnalemmicMammoth is Charles Sheffield's "The Spheres of Heaven"! Thanks again!

Hello all, I was thinking back on my scifi knowledge and I remember a lot of bits and pieces of a book I read in the 2000s (between 2004 - 2010). It may also be a series, but I thought it was a single book. The story was self contained.

The big details are:

• multiple civilizations discover a gate (manufactured structure or wormhole, I don't recall. I think it was an artificial wormhole),
• probes disappear, including manned craft,
• humans send a warship in, which is bad because its old and I believe a bunch of the people are prisoners of some kind. I remember them being ragtag, some died, and they didn't really know each other. I believe the cast was mostly humans with a delegation of aliens.
• emerge underwater not in space, which was a big plot point,
• crab-like species lives on the planet and are planning a reverse invasion because they have some leg up (I don't remember what) + they have mind control, which the protag sees one of the other humans get mind controlled,
• at the end/near the end, the human general (not the protagonist) monologues and confuses the alien leader, because he realizes that there is a time dilation difference between this planet and where they all came from. He knows he can buy time for his message to be sent back and for the human fleet to have prepared for this alien invasion

One of the big key things I remember was that there was a plantoid race that was actually some kind of symbiosis/parasite to a plant called, and they were called "Angel". I want to say it was a near-final-chapter reveal.

This sounds tropey, but I also remember that the races didn't care for the humans because they had a battleship to spare to beginwith/were warlike.

Thanks!

I crossposted to r/Scifi and got the answer. Im going to close the thread. Shout out to AnalemmicMammoth for the right answer, which is Charles Sheffield's "The Spheres of Heaven"!

Hello all, I was thinking back on my scifi knowledge and I remember a lot of bits and pieces of a book I read in the 2000s (between 2004 - 2010). It may also be a series, but I thought it was a single book.

The big details are:

• multiple civilizations discover a gate (manufactured structure or wormhole, I don't recall. I think it was an artificial wormhole),
• probes disappear, including manned craft,
• humans send a warship in, which is bad because its old and I believe a bunch of the people are prisoners of some kind. I remember them being ragtag, some died, and they didn't really know each other. I believe the cast was mostly humans with a delegation of aliens.
• emerge underwater not in space, which was a big plot point,
• crab-like species lives on the planet and are planning a reverse invasion because they have some leg up (I don't remember what) + they have mind control, which the protag sees one of the other humans get mind controlled,
• the human general monologues and confuses the alien leader, because he realizes that there is a time dilation difference between this planet and where they all came from

One of the big key things I remember was that there was a plantoid race that was actually some kind of symbiosis/parasite to a plant called an "Angel". I want to say it was a near-final-chapter reveal.

This sounds tropey, but I also remember that the races didn't care for the humans because they had a battleship to spare to beginwith/were warlike.