I read a story--the first part of one, at any rate--years ago, and haven't tracked it down since. It started with a man been sent to a planet under attack to pose as a monk--he arrived in the middle of an assault, but still had to do penance for being late. So he wore a hair shirt, that created an agonising reaction. He was captured by the attackers (who took him for the man he was posing as), who then stood off the planet in their starships and watched as a 'hell burner' weapon tumbled out of deep space and torched the planet. The attackers then explained that they weren't responsible for the hell burner, but every time they arrived at a planet, a hell burner turned up afterwards, at shorter and shorter intervals.
As the story developed, there was some kind of time travelling dimension, and a character turned out to have his organs reversed. I may have got some details wrong, but this was the shape of it.
Anyone know this story, and the author?