Swordsman of the Rift

Bryan Jenson is a former Marine who's been running from his past. When an acquaintance comes to him with a job, he takes it. He doesn't care about the pay or the job specifics. He just wants to escape the nightmares.
But in trying to run from his past, he runs into an even more terrifying nightmare when he and four others journey into the Rift Plains-a dimension connected to hundreds of other worlds. His party is overwhelmed and Bryan is taken prisoner.
Now he must team up with an archangel who has lost more than half her power and a low-level succubus to escape, get back at the woman who captured him, and defeat the Dungeon Master of this unknown world.
Simple, right?