Gate of Ivrel, an old sci-fi/fantasy mash-up by CJ Cherryh, whose work I've been really getting into lately. This is the first of the Morgaine Cycle sub-series in the Alliance-Universe series.
I'm about 75% through and loving it so far. There's very little action, its more of a character-drive story focusing on an agent from a futurist society (Morgaine) sent to a planet to close a series of gates used for intergalactic and time travel. She, along with 100 others she was sent with, were ambushed with her the only survivor. She goes through one of the gates herself in a desperate attempt to survive, and exits in what is to her only a few minutes, but in reality over 100 years have passed. She meets with Vanye, an outcast who killed his brother (in self-defense) who is terrified of Morgaine and the stories of old about her. She employs his help thanks to an ancient, honor-bound tradition, and the two set off to close the last gate at Ivrel.
Whatever tiny hope of correcting this died when Trump was re-elected. It's been game over for a while now. That's not to say we shouldn't try to make a difference where we can, but it's too late for Earth.