The Valley of Flames by Eva Chase

I thought I knew what I was fighting for. I thought I knew what I’d already lost. But it turns out the shrouded folk have been keeping a secret even more horrifying than I could have imagined.
To make up for my failure years ago, I’ll travel right into their hellish realm. I’ll sacrifice every happiness I’ve found and the men I’ve found it with. My life means nothing if I can’t see this mission through.
My men aren’t so willing to let me go, though, despite my past sins. And the game the shrouded folk are playing now has consequences that reach far beyond our little group. As the barriers between our world and theirs start to thin, will any of us make it out of this war alive?