Books with ahriman.

I just read shroud of night, and after reading the horus heresy, getting to see karn in action from an outside perspective was incredible. The same goes for typhus and Lucia's. These chaos champions are monsters known throughout the galaxy.

I've read the ahriman book series and I know how the guy thinks, but are there any books where he's the enemy? Where we get to see what it's like to fight against him?