The period for the Betrayal book is around the time when the Primarchs from four of the original Legions (i.e., Death Guard, Emperor's Children, Sons of Horus and World Eaters) have decided to turn traitor on the Emperor. There are no daemons or other such things from the Warp. A purging of these Legions takes place on the planet Ivstaan III where they kill all the Marines within their rank and file whom are still loyal to the Emperor. The third novel in the Black Library Horus Heresy series covers these events in great detail. Galaxy in Flames describes the virus bombing of Istvaan III and the Warmaster Horus' fall, which resulted in a galactic civil war where brother fought brother. In the virus choked wasteland of death and destruction that was once Istvaan III's Choral City, loyalist elements of the Luna Wolves, World Eaters, Emperor's Children and Death Guard Legions fight against the traitors of those Legions in a final display of defiance as the first part of the Heresy played out.
I finally got to play a couple games this weekend with my new Sons of Horus (SoH) army. I decided to use the trait that allows you to field veteran squads as troops so I can run a pure terminator army much like the conventional 40k Deathwing or Loganwing armies. Here is one of my current builds for a five man Legion terminator squad:
Sergeant - grenade harness, power axe, combi bolter
1x pair of lightning claws
1x power axe, heavy flamer
1x power axe, combi bolter
1x power fist, combi melta
Land Raider Phobos (dedicated transport - 2x twin linked lascannon, twin linked heavy bolter) - dozer blade, auxiliary drive, extra armor, ceramite plates
1) grenade harness counts as assault grenades for the squad
2) auxiliary drive ignores immobilization on a roll of 4+ on 1d6
3) ceramite plates - enemy melta weapons only roll 1d6 on armor penetration
The land raider also has a Machine Spirit and clocks in at 285 points, so you're definitely paying for the goodies.
One of the special rules for a SoH army is that each surviving model in their units get an extra attack at the end of each assault phase, however this does not count for unwieldy weapons such as a power axe. The terminator unit I posted above does not benefit much from this special rule except for the terminator armed with a pair of lightning claws. I prefer to take the AP2 melee weapons. So for my army this special rule is not all that beneficial. Many 40k armies have lots of special rules so I don't see this as overpowering. Just look at all the fantastic special rules for the new eldar and Tau in comparison.
All of my terminators wear suits of Cataphractii armor which confers a 4++ invulnerable save plus the Slow and Purposeful special rule. While I do like the better save I chose this type of terminator suit since it strictly adheres to the Legion's background as opposed to say a suit of Indomitus terminator armor.
I chose the heavy flamer as their special weapon since the main role of this terminator squad is dedicated to melee. You're going to score more wounds with the S5 template charging out of the land raider as opposed to either a plasma blaster or autocannon. The combi meltas help bring down tough multi wound models such as monstrous creatures and provide backup if needed to crack open an enemy transport so they can charge the contents.
My next article in this series will cover Justearin terminators.