To find out what the Horris heresy was go to the vaults of terra on youtube and look up the Horris heresy. In this fan fic which takes place in the warhammer 40k Lore the Death Korps of kierg is traveling in the warp when a warp storm pops up right there. And when some as small as a flicker has caused entire fleets to go out of sync or appear way of course chances of surviving were s 0.1%. But they did and when they emerged they were millenniums out of sync and were in imperium space right before the heresy so it became there plan to go to Darien storm the heretic governs base and prevent horris from being hit with the xenos sword. There was a problem though they were not a imperial guard regiment yet so the space wolves legion of the space which accompanied horris would attempt to stop them. When start they would already be en route to Darien.